« QuJctr / (/ PROCEEDINGS OF THE AMERICAN ACADEMY OF ARTS AND SCIENCES. VOL. XV. PAPERS READ BEFORE THE ACADEMY. RESEARCHES ON THE COMPLEX INORGANIC ACIDS. By Wolcott Gibbs, M. D., Rumford Professor in Harvard University. Presented June 24th, 1879. I propose the term " complex inorganic acid " for a class of com- pounds which may be considered as formed by the union of two or more acids with elimination of water in such a manner as to form a whole which in its chemical relations behaves like an acid containing a single radical. Compounds of this character were observed at an early period in the history of chemistry, but their real nature was for a long time entirely unknown, and our positive knowledge of the subject dates from the discovery of the silico-tungstates by Marignac in 1861.* Berzelius had long before described and analyzed a compound which we should now write 3 Si02 . 2 V205 . 2 P205 . 6 H20, the chemical relations of which are still to be studied.f He had also noticed the formation of peculiar yellow compounds when phosphoric or arsenic acids are digested with molybdic teroxide.t These were again noticed and partially studied by Svanberg and Struve,§ who * Ann. de Chimie et de Physique, (4,) iii. 55. t Lehrbuch der Chemie, iii. 3058. X Lehrbuch, iii. 1044. § K. Sv. Vet. Handlingar, 1848, p. 1. VOL. XV. (N. S. VII.) 1 1 PROCEEDINGS OP THE AMERICAN ACADEMY employed a solution of amnionic molybdate as a test for the presence of phosphoric acid. Sonnenschein* appears to have first shown that phosphoric oxide was an essential constituent of the yellow compound formed. Finally Debray assigned to the ammonium salt the formula 20 Mo03 . P,05 . 3 (MH4)20 + 3 H.,0, and separated the corresponding acid. In a paper presented to the Association of German Naturalists and Physicians in August, 1872, | Scheibler described salts of two different phosphotungstic acids, and gave formulas for the acids themselves, as well as for a sodium salt belonging to a third series, all of which, how- ever, he regarded as provisional. Since then nothing further has appeared upon the subject from Scheibler's pen, and I have conse- quently felt at liberty to include the phosphotungstates in my own work. My investigation of the complex inorganic acids had advanced but little before I found it necessary to study the alkaline salts of tungstic acid with special care. This study has alone occupied a great deal of time, and has proved one of extraordinary difficulty, in spite of the previous labors of Laurent, Lotz, Scheibler, Zettnow, Marignac, and others. The difficulties in question are mainly these : — 1. The alkaline tungstates are numerous and unusually complex. Salts of essentially different formulas approach so closely in percentage composition, that the differences lie very near the unavoidable errors of analysis. Thus Scheibler maintains that the formula of a particular sodium salt is 7WOr 3Na,0 + 16 aq, while, according to Marignac, the same salt must be represented by 12W03 . 5Na20 + 28 aq. The analyses are hardly sufficiently close to decide the question upon purely analytical grounds. 2. Almost all the alkaline tungstates are efflorescent in a very marked degree. 3. The salts of one series agree so closely in chemical properties with those of the next, that distinctive tests are wanting, and analysis does not always suffice to distinguish two salts even when unmixed. Mixtures are naturally very hard to deal with. * Journal fiir Prakt. Chemie, liii. 342. t Beriehte der Deutschen Chem. Gesellschaft, v. 801. OP ARTS AND SCIENCES. 6 4. Monoclinic and triclinic forms predominate very largely, but owing to rapid efflorescence it -is very difficult to make good measure- ments of crystals. The resemblance between the forms of different compounds is frequently very close. 5. Many salts are decomposed by boiling, or even by hot, water, yielding two or more different salts in solution. These usually re- combine in the act of crystallization or on cooling the solution, but the reactions of hot and cold solutions are often, as I shall show, very different. In determining the tungstic oxide in these compounds, I have em- ployed the method of Berzelius with mercurous nitrate almost exclu- sively, but I have modified the process slightly so as to gain materially in accuracy. To the hot solution of the tungstate mercurous nitrate is added until in small excess. Mercuric oxide, prepared by precipitat- ing the chloride by sodic hydrate, is then added until the yellow mer- curous tungstate takes a reddish hue which is persistent after boiling. If the solution is boiled before filtering it clears rapidly, and the pre- cipitate becomes rather more compact. The filtration and washing are then very easy and expeditious. The precipitate must be ignited as long as it loses weight. By this process Dr. Gooch, my assistant, obtained results which in two successive analyses of the same prejia- ration rarely differed by 0.1%. The water determinations were al- ways made by simple ignition. They almost invariably agree within a few hundredths. In the greater number of cases the alkaline base was determined from the loss, as the results obtained in this manner are far more accurate than those yielded by the direct method. But in some doubtful salts the alkali was determined directly. Ammonia was always estimated by boiling the compound with an excess of sodic hydrate, collecting the ammonia in chlorhydric acid, and weigh- ing it as chloride. The ouly objection to the method of determining tungstic oxide above given is, that the precipitate of mercurous tungstate is rather voluminous, so that it is necessary to work with quantities of alkaline tungstate not mucli exceeding one gramme in weight. I endeavored to overcome this difficulty by omitting the mercuric oxide and evapo- rating the solution and precipitate, after the addition of mercurous nitrate, to perfect dryness in a water bath, continuing the heat until all the free nitric acid was expelled. This method gave results which corresponded very closely with those obtained by the use of mercuric oxide to neutralize the free nitric acid, and in consequence of the extremely compact form of the dry mercurous tungstate, permitted the 4 PROCEEDINGS OF THE AMERICAN ACADEMY employment of much larger quantities of salt for analysis. On the other hand, it presents another difficulty, arising from the fact that the dry mercurous tungstate adheres with excessive tenacity to the evapo- rating vessels, whether of glass, porcelain, or platinum, so that the first method is on the whole to he preferred. The separation of tungstic oxide from other bases is best effected by fusing the salt with an excess of potassio-sodic carbonate and dis- solving out the alkaline tungstates formed. Normal sodic tungstate has long been known, and all the analyses concur in assigning to it the formula WQ4Na2 -f- 2 aq. It is now to be had from various German firms in a state of purity, and forms the most convenient material for the study of the com- pounds of tungsten. The acid salt analyzed by Anthon, and to which the formula W2O.Na2 -f- 4 aq was long ascribed, is now well known to have an entirely different composition ; but Lefort* has recently endeavored to show thatditung- states and tritungstates really exist, and has described a number of salts of each series. Lefort obtains sodic ditungstate by adding glacial acetic acid to a saturated solution of the neutral salt until the reac- tion with litmus becomes acid. After a day or two the salt separates in long prismatic crystals, with the formula W2O.Na2 -f 6 aq. I have repeatedly attempted to prepare the ditungstate by this process, but without success in any one instance, the resulting salts being, as I shall show further on, in all cases very different in compo- sition. Lefort prepared sodic tritungstate by pouring a concentrated solution of the ditungstate into a boiling solution of glacial acetic acid. His analyses agree fairly well with his formulas, and I have adopted his results without question, in the belief that my own inability to reproduce them was due to the omission in his paper of some matter of detail which appeared insignificant, but which was really important. Ten to Four Sodium Salt. — The salt to which I have given this name appears to have been first observed by Forcher,t who obtained * Ann. de Chimie et tie Physique, (5,) ix. 93. t Wiener Aka 248 8.32 8.13 8.21 8.50 8.18 8.50 8.16 8.39 23H.,6 414 13.88 13.88 13.94 13.70 13.93 13.70 13.88 13.53 wo3 NajO H20 78.27 8.37 15.36 77.63 8.16 14.21 77.80 8.32 13.88 77.86 8.30 13.83 2982 100.00 99.86 99.80 The means of all these analyses may be compared with the three formulas above given. For the ratio 10 . 4 . 22 " 10 . 4 . 24 " 10 . 4 . 23 Means of new analyses, The analyses therefore leave no reasonable doubt as to the true constitution of the salt. The solution of the 10 : 4 sodic tungstate has a distinct acid reaction, but it is very difficult to determine the limits of the basicity in this series, because no salts could be obtained having a number of molecules of fixed base higher than four. On the other hand, the white insoluble mass obtained by igniting the crystalline hydrate must have the formula 10 WO, . 4 Na^O, and I consider it a true pyro-salt. When boiled for some time with water, the pyro-salt dissolves and the original salt crystallizes from the solution. The case appears to be exactly analogous to that of sodic metatungstate, the insoluble 4 W03 . Na20 of Scheibler and Marignac, giving the normal sodic metatungstate, 4WO, . Na20-f 10 aq, when heated with water in a sealed tube. The reactions of the 10:4 salt with metallic solutions are extremely similar to those of the 12 : 5 salt, 12W03. 5Xa20-f 28 aq, OP ARTS AND SCIENCES. ( so that in fact it is difficult to distinguish between the two in any other way than by the habitus of the crystals and by analysis. When the 10:4 salt is dissolved in water and a current of sulphydric acid gas passed into the solution to the point of saturation, the liquid becomes at first yellow, and finally orange red. On standing or evapo- ration, it deposits brown tungstic sulphide, WS3, and the still faintly yellow mother liquor gives fine colorless triclinic crystals, which are separate and distinct, not twinned or aggregated in masses like the 10:4 salt. These crystals after recrystallization have the formula of the 12:5 salt presently to be described, namely, 12Wo3.5Na20 + 28 aq, as the following anatyses show : — 1.6491 gr. gave 1.2760 gr. W03 = 77.38% 2.3696 gr. lost 0.3308 gr. water = 13.96% 2.0037 gr. " 0.2790 gr. " = 13.92% Calc'd. Found. 12W03 2784 77.38 77.38 5Na20 330 8.61 8.68 28Ho0 504 14.01 13.92 13.96 3618 100.00 The formation of the 12:5 from the 10:4 salt is easily explained, as well as the separation of the tungstic sulphide, since we have 2 (10 W03 . 4 Na20) + 5 H2S = 12 W03 . 5 Na20 + 3 W03 . Na90 4-5WS. + 5 H20. A concentrated solution of the 10 : 4 sodium salt is resolved by boiling into the 12:5 salt and other compounds difficult to isolate in a state of purity. When a hot solution of potassic bromide or nitrate is added to a boiling solution of the 10:4 sodium salt, a white crystalline precipi- tate is speedily formed, which has the formula 12W03.5K20 + 10 aq. But if a cold solution of a potassic salt is added to a cold solution of the 10 : 4 sodium salt, a white crystalline precipitate is formed, which has the formula 10 W03 . 4 K20 + 9 aq. 8 PROCEEDINGS OF THE AMERICAN ACADEMY Twelve to Five Sodium Salt. — This is the salt to which Scheibler gives the formula 7W08.3Na20+16aq, and which Marignac writes 12W03. 5 Na20 -f 28 aq. According to Lotz, the salt contains fourteen atoms of water in place of sixteen as found by Scheibler. I have adof)ted the formula of Marignac, which agrees best with the analyses. In preparing this salt I have employed Scheibler's method, which consists in nearly neutral- izing a boiling solution of the neutral tungstate, W04Na2 -\- 2 aq, by chlorhydric acid. When the proper quantity of chlorhydric acid is added, the 12:5 salt is formed at once, and crystallizes from the solution in large colorless crystals, which, according to Scheibler, are mono- clinic ; according to Marignac, triclinic. If the proportion of chlor- hydric acid is just sufficient to give an onion-red reaction with litmus, crystals are obtained, which are either a combination or a mixture of equal molecules of the 10:4 and 12:5 salts. These crystals are, accord- ing to Dr. Gooch, triclinic; their habitus resembles that of the 12:5 rather than that of the 10:4 salt. In this salt, in two different prepa- rations carefully dried and pressed with woollen paper, H f 1.2546 gr. gave 0.9725 gr. W03 = 77.51 % j 1.2320 gr. " 0.9554 gr. " = 77.55% 1.4G80 gr. lost 0.2035 gr. water = 13.86% [1.7511 gr. " 0.2431 gr. " =13.88% f 1.0842 gr. gave 0.8407 gr. W03 = 77.54% 1 1.0908 gr. " 0.8450 gr. " =77.47% " 1 1.6919 gr. lost 0.2362 gr. water = 13.96% [ 1.5259 gr. " 0.2125 gr. " =13.93% The analyses agree closely with the formula 12 WOa . 5 Xa.O 4- 10 W08 . 4 Na20 -f 51 aq, or, which requires 22 WO, 5104 9 Na.,6 558 51 H.,6 918 22W03 Calc'd 77.57 8.48 13.95 . 9 Xa2< Mean 77.52 8.57 13.91 3 + 51 77.51 aq, Eound. 77.55 77.54 77.47 13.86 13.88 13.96 13.93 6580 100.00 100.00 OP ARTS AND SCIENCES. 9 I have already stated, that in repeated trials I had not been able to obtain the sodic ditungstate described and analyzed by Lefort, though the process given by him was followed implicitly. In one experiment the crystals obtained gave on analysis results which correspond closely with the formula 12W03.5Na20 + 28aq. 1.9868 gr. lost on ignition 0.2786 gr. water = 14.02% 1.2870 gr. " " 0.1806 gr. " =14.01% 0.9365 gr. gave 0.7243 gr. W03 = 77.34% 1.3560 gr. " 1.0483 gr. " =77.31^ Found. 77.34 77.31 8.66 14.02 14.01 In this experiment the normal tungstate was dissolved in cold water to a very strong solution, glacial acetic acid was added in excess, and the whole allowed to stand for twenty-four hours, when prismatic crystals separated. In a second experiment a concentrated solution of sodic tungstate was heated to the boiling point and ordinary acetic acid added in excess. Alcohol then threw down a pasty mass, which, after re-solution in water and crystallization, gave on analysis results which corresponded with the formula 22W03. 9 Na20 + 51 aq. Calc'd. 12W03 77.38 5Na20 8.61 28H20 14.01 100.00 1.0861 gr. lost on ignition 0.1492 gr- water = 13.74% 1.3830 gr. " 0.1895 gr. " = 13.70% 0.8884 gr. gave 0.6899 gr. wo3 = 77.66% 1.2746 gr. " 0.9902 gr. " = 77.69% Calc'd. For md. 22 WOs 77.57 77.67 77.69 9Na26 8.48 8.60 51II26 13.95 13.70 13.74 100.00 The small differences between the calculated formula and the direct results of the analyses, in this instance, are exactly such as would be produced by the admixture of a small percentage of the 10:4 sodium salt, which, as I have shown above, is formed when a solution of neutral sodic tungstate is boiled for some time with an excess of acetic acid. 10 PROCEEDINGS OP THE AMERICAN ACADEMY The general result of my own study of the action of acetic acid upon the neutral tungstate is, that we obtain the 12 : 5, the 22: 9, or the 10:4 salt, according to the circumstances of the case, the constitution of the salt formed depending mainly upon the degree of concentration of the acid and upon the duration of its action. These results are in no way inconsistent with those of Lefort, and his analyses seem to leave no reasonable doubt that he obtained various salts to be classed as ditung- states and fcritungstatea. Potassic Tuvgstates. — When a hot solution of the 10 : 4 sodium salt is mixed with a hot solution of potassic nitrate, a white precipitate shortly appears in small colorless crystalline scales, which may lie re- crystallized by projecting them in very small quantities at a time into boiling water. This method, which was first given by Scheibler, enables us to redissolve the salt in water without loss from the exces- sively violent succussions which occur on heating the salt with water in the usual manner. The salt requires a rather large quantity of water for solution, and crystallizes almost completely from the cold liquid. Of this salt in the first preparation, — 0.9888 gr. lost on ignition 0.0510 gr. water = 5.18% 0.6513 gr. " " 0.0358 gr. " = 5.49% 1.1663 gr. " a 0.0610 gr. " = 5.23% 1.1287 gr. " u 0.0596 gr. « = 5.28% 1.0068 gr. gave 0.8173 gr. W03 = 81.21% In a second preparation, — 1.4312 gr. lost on ignition 0.075] gr. water = 5.25% 1.5846 gr. " 0.0832 gr. " = 5.25% 0.5786 gr. gave 0.4686 gr. W03 = 80.99% 0.4773 gr. " 0.3875 gr. " = 81.20% 1.8957 gr. " 1.5370 gr. " = 81.08% These analyses lead to the formula 12 W03 . 5 Kp + 10 aq, which requires : — Calc'd. Mean. Found. 1. 2. -, 12W03 2784 81.02 81.12 81.21 80.99 81.20 81.08 5 1^0 472 13.73 13.62 10 H^O 180 5.25 5.26 5.29* 5.25 5.25 . . . 3436 100.00 Mean of the four determinations of water in the first preparation. OP ARTS AND SCIENCES. 11 Marignac gives eleven molecules of water. Scheibler gives the formula 7 W03 . 3 K20 -f- 6 aq, but his analyses agree better with that of Marignac. When normal potassic tungstate, W04K2, is evaporated to dryness with boric hydrate, and the soluble salts are washed out from the mass, a salt is obtained which after recrystallization has the formula 10WO3 • 4K20 + 9aq. The same salt is formed when cold solutions of potassic nitrate or bro- mide are added to cold solutions of the 10:4 sodium salts. It resembles the 12:5 potassium salt, already described, so closely, that it is difficult to distinguish between the two. This salt has not been described by other writers upon the subject. In preparation a, from the action of boric acid upon normal potassic tungstate, 0.4566 gr. gave 0.3714 gr. W08 = 81.34% 0.5915 gr. lost on ignition 0.0331 gr. water = 5.59% . In preparation b, from the action of acetic acid upon the normal potassium salt, 0.7418 gr. gave 0.6024 gr. W03 = 81.21% 1.1104 gr. lost on ignition 0.0610 gr. water = 5.49% 0.7060 gr. gave 0.5736 gr. W03 = 81.27% 1.0266 gr. lost on ignition 0.0556 gr. water = 5.42% These analyses correspond best with the formula IOWO3. 4K20 + 9aq. Calc'd. Mean. 0WO3 2320 81.13 81.27 81.34 81.2 81.27 4K20 377.6 13.20 13.23 13.07 13.30 13.31 9H20 162 5.67 5.50 5.59 5.49 5.42 2859.6 100.00 It is probable that the salt had lost a little water by efflorescence. When normal potassic tungstate is dissolved in boiling water, it is decomposed into free alkali and 12 : 5 acid tungstate. The decomposi- tion may be represented by the equation, 12 (W03 . K20) + 7 II20 = 12 W03 . 5 K20 + 14 KHO. In the acid salt formed in this manner, 0.7738 gr. lost on ignition 0.0414 gr. water = 5.35% 1.0385 gr. gave 0.8411 gr. W03 = 80.99% 12 PROCEEDINGS OF THE AMERICAN ACADEMY The formula 12 WOg . 5 K20 -4- 10 aq requires 81.02% W03 and 5.25% H20. Amnionic Tungstates. — When a solution of amnionic chloride is added to one of the 10:4 sodic tungstate, beautiful white talcose scales are thrown down, which are but slightly soluble in cold water. After washing, they may be dissolved in boiling water without evolution of ammonia and recrystallized. The analyses of this salt agree fairly well with the formula 10 WOs . 4 Xa/J + 4 {10 WO, . 4 (NHJ20) -4- 50 aq, as the following analyses show : — j ( 0.5058 gr. gave 0.4851 gr. WO, = 85.74 % ( 0.5602 gr. loston ignition 0.0690gr. water and ammonia = 12.31 % S 0.3346 gr. ' t 0.3849 gr. lost 0.0427 gr. " = 12.77% gave 0.3294gr. wo, = 85.59% Calc'd. Mean. Found. 50 WOa 11600 85.42 85.62 85.74 85.59 4 Na.,0 248 1.83 1.79 1.94 1.64 16 (NH4)20 50H2O 832 900 6.12 I 6.63 ) 12.54 12.31 12.77 13580 100.00 99.95 Analyses (I.) and (II.) are of different preparations of the same salt. When commercial ammonic tungstate (containing a little sodic oxide) is dissolved in ammonia, and acetic acid is added to the filtered liquid, a white slightly soluble salt is obtained which after recrystal- lization has the formula 12 WO, . 0(NH4)20+ 6aq. In this salt : 0.9293 gr. lost on ignition 0.1087 gr. = J lh69% NH,andH20 188.31% WO, 0.5366 gr. " « 0.0626 gr. = f H-6C% XH, and IlvO (88.34% W(); 0.6602 gr. gave 0.2039 gr. platinum = 8.15% (NH4)20 1.1241 gr. « 0.3370 gr. " = 7.92% Calc'd. Mean. Found. 12 WO, 2784 88.32 88.32 88.34 88.31 5(NH4)20 260 8.24 8.03 8.15 7.92 6H20 " 108 3.44 3.64 3.51 3.77 3152 100.00 99.99 OP ARTS AND SCIENCES. 13 Marignac found in this salt five molecules of water. Lotz and Scheibler gave it the formula 7 W03 . 3 (NH4)20 + 3 H20. Marignac has also described and analyzed an ammonium salt to which he gives the formula 5 W03 . 2 (NH4)20 + 5 H20. I should double this formula, and write it 10 W03 . 4 (NH4)0 + 10 H20, so that it would then belong to the series of 10:4 salts, the existence of which I have endeavored to establish. According to Marignac, it breaks up by solution in water into the 12:5 and 8 : 3 salts. 2{10 W03 . 4(NH4)20} = 12 WO, . 5(NH4)20 -f 8 W03 . 3(NH4)20. Zinc Salts. — When a solution of zincous sulphate is added in small excess to a hot solution of the 10: 4 sodic tungstate, no precipitate is produced at first, but after a few seconds beautiful aggregates of white needles make their appearance, and continue to be deposited for some time. They are almost perfectly insoluble in boiling water. For analysis they were washed with cold water and dried in pleno over sulphuric acid. The zinc salt is soluble both in an excess of zincous sulphate and of sodic tungstate ; hence the precipitate which is at first formed is instantly redissolved and does not become permanent until a small excess of the sulphate is added. In this salt, 0.3342 gr. lost on ignition 0.0349 gr. water = 10.44% 0.6392 gr. gave 0.5128 gr. W03 = 80.50% 1.0205 gr. " . 0.8200 gr. " =80.35% These analyses correspond with the formula 6W08 . 2ZnO + 10 aq. Calc'd. Found. 6W03 1392 80.27 80.50 80.35 2ZnO 162 9.34 9.14 (loss) 0H2O 180 10.39 10.44 1734 100.00 From this it appears that the zinc salt is formed by the decomposi- tion of the 10 : 4 sodic tungstate. The result may be expressed by the equation, 14 PROCEEDINGS OF THE AMERICAN ACADEMY 10 W08 . 4 Na90 -4- 4 S04Zn = 6 W03 . 2 ZnO + 2{2 W08 . ZnO} -f 4S04NiV The zincous ditungstate, as Lefort has shown, is readily soluble in water and remains in solution. When a cold solution of zincous sulphate is added to a cold solution of the 10:4 sodium salt, a different result is obtained. A white precipi- tate is at first formed as before, which instantly redissolves. After a small excess of the sulphate has been added, the solution gives in a short time colorless needles of a second zinc salt. Like the 6 : 2 salt first described, this is insoluble in water, cold or hot, but readily dis- solves in an excess of the tungstate or sulphate. When a large excess of the sulphate is present, the zincous tungstate does not separate from the solution. Of this salt in one preparation, dried over S04H2 : 0.6586 gr. lost on ignition 0.0706 gr. water = 10.72% 0.5894 g, gave 1 0.0638 gr. ZnO =10.82% s S 1 0.4606 gr. W03 =78.16% These analyses lead to the formula 10WO8 . 4ZuO-f 18 aq, vhich requires Calc'd. Found. 10 wo3 2320 78.16 78.16 4 ZnO 324 10.92 10.82 18H20 324 10.92 10.72 2968 100.00 99.70 In a second preparation of the same salt, dried by woollen paper, 1.0006 gr. gave by ignition 0.1663 gr. water, also 0.7322 gr. W03 and 0.1048 gr. ZnO = 16.62% water, 73.1 8 % W03, and 10.47% ZnO. results correspond to the formula 10WO3.4ZnO + 29 aq, which requires Calc'd. Found. 10 wo3 2320 73.27 73.18 4 ZnO 324 10.24 10.47 29H20 522 16.49 16.62 3166 100.00 100.27 When a cold solution of zincous sulphate is added to a cold solu- tion of the 22-atom sodium salt a precipitate is formed, which re- OF ARTS AND SCIENCES. 15 dissolves precisely as in the last-mentioned cases. After the solution of zinc has been added in small excess, white needles separate, which are insoluble in water, and have the formula 22 W03 . 9 ZnO + 66 aq, as the following analyses show : 1.4620 gr. gave 0.2509 gr. water on ignition, 1.0602 gr. W03 and 0.1508 gr. ZnO = 17.16% water, 72.52% W03, and 10.31% ZnO. Calc'd. Found. 22W03 5104 72.69 72.52 9 ZnO 729 10.38 10.31 66H20 1138 16.93 17.16 7021 100.00 99.99 The salt was dried for some time upon woollen paper. General Conclusions. — From my own investigations, as well as from those of other chemists who have preceded me, I arrive at the fol- lowing classification of the alkaline tungstates as most nearly repre- senting the present state of our knowledge. There are three series of salts, which may be termed respectively normal tungstates, meta- tungstates, and pyro-tungstates. The two first-named series may be represented by the following as typical salts : — Normal Series. W03 . Na20 -f 2 aq 2 W03 . Na20 -j- 6 aq Lefort. 3W03.Na20 + 4aq Meta- Tungstates. 4 W03 . Na20 + 10 aq or W40„(NaO)3 -f- 10 aq Scheibler 6 W03 . 2 BaO -f 12 aq " W6016(Ba02)2 -f- 12 aq « 8 W03 . 3 (NH4)20 + 8 aq " W8021'(NH40)6 -f- 8 aq Marignac. 10 W03 . 4 Na20 + 23 aq " W10O26(NaO)8 + 23 aq 12 W03 . 5 Na20 -j- 28 aq " W12O31(NaO)I0 -f- 28 aq Marignac. 14 W03 . 6 Na20 -j- 42 aq " W14036(NaO)]2 + 42 aq The salts of the normal series require no special notice. As already stated, I have not succeeded in preparing the di- and tri-salts of Lefort, but there seems to be no reason to doubt their existence. The pyro-salts are obtained from the meta-salts by ignition, as insoluble crystalline masses, which are decomposed by long boiling with water. All the 16 PROCEEDINGS OF THE AMERICAN ACADEMY meta-tungstates with an alkalin-e base, appear to contain water of constitution and to have an acid reaction, but it is difficult to deter- mine the quantity of basic hydrogen with certainty, and the mere fact that the salts have an acid reaction is not in itself conclusive evidence that they are in the strict chemical sense acid. Tungstates have been described by different chemists, which do not fall within either of the groups given above. In all these cases, however, it will be found on examination, that the analyses do not agree well with the formulas assigned, and that there is reason to believe that the salts studied were mixtures. I consider it at least probable that the tri-salts of Lefort belong in reality to the meta-series, their molecular weights being doubled. But it is of course possible that we have here cases of isomerism, and I much regret that I did not succeed in obtaining these salts for study and comparison. With respect to the double salt which I have described above, and which has the formula 12 W03 . 5 Na20 -f- 10 W03 . 4 Xa20 -f- 51 aq, I may remark that it is possible that the compound is really 22 W03 . 9 NajO + 51 aq, and that it is not a double salt, but one term in a series which we obtain by again doubling the formulas of the meta-tungstates as I have given them above. The question is one which I must leave un- decided for the present at least. The analogy between the compounds of tungsten and molybdenum is in general so great, that we ought to expect to find alkaline molyb- dates corresponding to the three series of tungstates. We owe to Ullik the most complete examination of the molybdates which has been published. A careful study of his results will show that, while we have a number of molybdates to which there are apparently no cor- responding tungstates, we have at least reason to believe in the exist- ence of the three series of normal, meta, and pyro salts. Thus the following salts may be assumed as typical : — Normal Series. M0O3 . Na20 + 2 aq 2 Mo03 . Na20 and with 1 . H20 Meta Series. 4Mo03 . Na2° + 6a(l or Mo4On(NaO)2 -f 6 aq 6 Mo03 . 2 NagO -+- 1 4 aq " Mo,.0lt.(NaO)4 -f- 14 aq 8 M0O3 • Na20 . 2 H.0 -f 2 aq « Mog021'(NaO)2(HO)4 -j- 2 aq OP ARTS AND SCIENCES. 17 10 Mo03 • Na2° • 3 H2° + 9 a(i or Mo10O26(NaO)2(HO)6 4- 9 aq 14 Mo08 . 6 Na20 -f- 44 aq " Mo1403B(NaO)12 + 44 aq 16 M0O3 . 2 Na20 . 5 H20 + 3 aq " Mo16O41(NaO)4(HO)10 -f 3 aq 18 M0O3 . 2 BaO . 6 H26 -f 2 aq " Mo1804G(Ba02)2(HO)12 -j- 2 aq It may of course be maintained that the arrangement of the acid salts of molybdic oxide which I have adopted is purely arbitrary, and that they might be written with equal or greater probability in the usual manner, as members of the normal series, which would then be : Mo03 . Na20 + 2 aq 8 Mo03 . Na20 + 2 aq 2 M0O3 . Na20 -f aq 9 Mo03 . BaO -j- 4 aq 3 M0O3 • Na2° + 7 aq 10 M0O3 . Na20 -j- 12 aq 4 Mo08 . Na20 -j- 6 aq 16 Mo03 . Na20 + 9 aq. To this I reply that one arrangement is no more arbitrary than the other, since we have no positive knowledge of the constitution of these salts, their molecular weights being, as in the case of most inor- ganic compounds, entirely unknown. The commonly received view is therefore also a pure assumption. In any case, however, we have the two salts, represented respectively by the formulas 4 Mo03 . Na20 -f 6 aq or Mo4On(NaO)2 -f 6 aq 1 4 Mo08 . 6 Na20 -4- 44 aq " Mo14036(NaO )~2 + 44 aq, forming the upper and lower limits of a molybdic series corresponding to alkaline tungstates, and from these we may fairly infer the exist- ence of the intermediate compounds. But one acid tungstate of the meta series is at present known, the salt 8 W03 . Na20 '4- 12 aq, or W8023(NaO)2 -f 12 aq. This may be considered as an acid salt of the 8-atom term, and written 8 W03 . Na20 . 2 H20 + 10 aq, so that it will correspond to the molybdic salt 8 Mo03 . Na20 . 2 H.,0 + 2 aq. But the supposition that acid metatungstates of the 4 : 1 series really exist, is in no way inconsistent with the view of the whole subject which I have taken. So far as I know, no attempt has been made to exhibit the mode of union of the elements in the higher tungstates. Our views of the subject will differ according as we consider tungsten vol. xv. (n. s. vii.) 2 18 PROCEEDINGS OP THE AMERICAN ACADEMY as tetratomic or hexatoroic. In what follows I have adopted the latter hypothesis, partly because the hexatomic character of tungsten is well marked in various compounds, as for example in WC1C, and partly because the graphical representations are, on the whole, simpler. More- over, if we consider tungsten to be tetratomic in the normal series, we obtain a reason for the existence and peculiar character of the meta series, by supposing that in this the metal is hexatomic. We may, to begin with, represent sodic metatungstate, 4 W03 . Na20, as follows : wos = wo2 , \ / 1 o ' 0 o 1 I Na - O - W02 = WO, - O - Na The next term in the series, 6 WO,., . 2 Na20, will then be wo2 = wo2 o o Na - O - W02 — W02 - O - Na i I 0 o 1 I Na - O - WOa = WO, - 0 - Na The third term, 8 W03 . 3 Na20, may be represented by the graph- ical formula WO, = wo2 \ / 1 o ' Na - O - W02 — W02 - O - Na O O Na - O - W02 — W02 - O - Na i i 0 o 1 I Na - O - W02 = W02 - O - Na and so on for the other known terms, the highest, 14 W03 . 6 Na20, being represented by the expression OF ARTS AND SCIENCES. 19 W02 = W02 I I Na - 0 - W02 — WO, - O - Na Na - O - W02 — W02 - O - Na 0 O 1 I Na - O - W02 — W02 - O - Na I " I 0 o 1 I Na - O - W02 — W02 - O - Na I ! o o Na - O - W02 — WO,, - O - Na i i 0 o 1 I Na - O - W02 = W02 - O - Na It will be seen that, with this view of the subject, those terms in the series in which the number of atoms of sodic oxide is even are repre- sented by formulas in which the free atoms of W02 are united, in part directly, and in part by oxygen, while the union is direct when the number of atoms of sodic oxide is odd. I shall return to this subject in speaking of the phosphotungstates and other complex inorganic acids. No great value can, in the present state of our knowledge, be attributed to formulas like the above. They afford, however, some assistance in showing the possible mode of formation of the different terms of the series, but various other constructions may be devised which are perhaps equally probable. In adopting provisionally the particular construction which I have used, I have simply followed the clew given by the commonly received formula for potassic dichromate, Cr02 - O - K O Cr02 - O - K, which of course gives a similar expression for the homologizing term in the acid tungstate series. So far as I am aware, no attempt 20 PROCEEDIx\GS OF THE AMERICAN ACADEMY has been made to formulate the remarkable compounds of tungsten described by Wohler and others, and which may be exjjressed empiri- cally by the formulas WgC^Najj, and W5014Na,. If we double these formulas, we may bring them into harmony with the series of acid tungstates by writing them respectively, WO_, = AYO, Na - O - WO, — W02 - O - Na I i o o and Na - 0 - W02 = WOa - O - Na, woa = woa II II wo2 — wo, II II wo, — wo2 0 o 1 I Na - O - WO, — WO, - O - Na I l o o Xa _ O - WO, — WO, - O - Na. These formulas, if like the others purely hypothetical, have at least the merit of explaining the production of the insoluble sodium salts in a simple and natural manner. They are also entirely consistent witli the simplest view which we can adopt with respect to the consti- tution of the blue oxide of tungsten, which is commonly written W205, but which is much more probably W4O10, and structurally wo2 — wo2 o o WO, — wo2. The progress of science tends to show that the constitution of inor- ganic compounds is more complex than would at first appear. It would not be difficult to multiply instances which support this view, OF ARTS AND SCIENCES. 21 but I shall content myself with citing. a single case, which has not been discussed, and which, strangely enough, has attracted but little attention. I refer to the remarkable series of compounds of molyb- denum studied by Blomstrand* and by Atterberg.f Representative terms in this series are expressed by the formulas Mo8Cl4 • Cl2 Mo3Cl4 . (OH)2 MosCl4 . Br2 Mo,Br4 . Br2 Mo3Br4 . (OH)2 Mo8Br4 . S04 omitting water of crystallization for greater brevity. The action of alkalies upon the bromide Mo3Br4 . Br2 produces first MoaBr4 . (OH)2, and afterward Mo3(OH)4(OH)2, or Mo3(OH)6, the hydrate of the pro- toxide of molybdenum, usually written MoO . OH2, or Mo(OH)2. There is therefore good reason to believe that the lowest expression for this hydrate is Mo3(OH)6, the structural formula of the cor- responding bromide being, perhaps, Mo = Br2 Mo = Br2 Mo = Br2. In this formula the end atoms of molybdenum are tetratomic, and the middle atom hexatomic, which will perhaps explain the fact that there are but two movable atoms of bromine in a whole series of salts. If molybdic protoxide is Mo303, it is probable that the teroxide is not MoO.{, but rather some higher multiple of this expression, and we may extend the inference to WO., also. With these preliminaries, I pass to the special subject of my work. * Journal t'ur prakt. Chemie, lxxxii. 436. t Nagra bidrag till Kannedomen om Molybden, Stockholm, 1872, p. 16. ( To he continued.) * 4 NK> Xr z~4 i^—< ~j~ Jfc QuJfcz— - L. ■> OF ARTS AND SCIENCES. 109 VI. RESEARCHES ON THE COMPLEX INORGANIC ACIDS. By Wolcott Gibbs, M. D., Rumford Professor in Harvard University. (Continued from Vol. XV. p. 21, June, 1879.) Presented June 25th, 1880. PHOSPHO-TUNGSTATES. The phospho-tungstates, as already stated, were discovered by Scheibler, who gave provisional formulas for several different compounds. As the German chemist has published nothing farther upon the subject for six years, and as the study of these compounds seemed to be a necessary preliminary to that of other complex inorganic acids, I have devoted much time and labor to them. The investigation has proved very difficult and tedious, but has yielded results which, if not in all cases perfectly definite and conclusive, are yet as I think valuable and interesting. The difficulties met with in the study of this class of salts are in some respects analogous to those which present them- selves in the case of the alkaline tungstates. They are mainly as follows : — 1. The normal alkaline phospho-tungstates are readily decomposed by water, yielding acid salts which are often very complex. These acid salts are very slightly soluble, and cannot in general be recrystal- lized for analysis. They are formed in greater or less proportion whenever we attempt to purify the neutral or less acid salts by re- crystallization. In many cases the ratio of tungstic and phosphoric oxides in the neutral salt is changed when the acid salt is formed, so that we can draw no certain conclusion from the constitution of one salt as to that of the other. It is usually very difficult, or even impos- sible, to pass from the acid back to the primitive normal or neutral salt, because the addition of an alkali produces new compounds. 2. It is difficult by any analytical method which has been devised to determine the percentage of phosphoric oxide with great accuracy, 110 PROCEEDINGS OP THE AMERICAN ACADEMY and very small differences — often not exceeding 0.2% — are some- times sufficient to change the ratio hetween the number of atoms of phosphoric and tungstic oxides. In the case of tungstic oxide the divisor which we must employ (W03 = 232) is so large that a very sensible variation in the percentage of the oxide does not sensibly affect the quotient. It is consequently sometimes difficult to decide between formulas in which, for example, the ratios of the two oxides are as 24 : 1, as 22 : 1, or as 20 : 1. 3. For similar reasons it is very difficult to recognize mixtures of different salts. 4. The alkaline phospho-tungstates are usually efflorescent, — fre- quently to a remarkable degree. 5. The salts 'of the different series agree so closely in physical and chemical properties that, as in the case of the tuugstates, distinctive tests are not to be found. 6. It is almost impossible to predict what compound will be formed when tungstates and phosphates or phosphoric acid are mixed, even when the mixture is made with the greatest care and in perfectly definite proportions. Very small variations in the conditions of the process materially affect the results. 7. A large proportion of the salts of this series crystallize only from sirupy solutions, and are consequently difficult to purify by recrystallization. 8. When new salts result from a double decomposition the phospho- tungstate formed does not often correspond in composition to that from which it is derived. It may be of a higher or of a lower order. Preparation and General Properties. — Scheibler prepared the salts which he has described by boiling neutral or acid sodic tungstates with half their weight of phosphoric acid. I have found it more convenient to employ the following methods. Solutions of neutral sodic- tungstate, W04Na., -|- 2 aq, and of hydro-disodic phosphate, P04Na2H -j- 12 aq, in the proportion of n molecules of the former to m of the latter, are to be boiled together for some time. The solution has a very strong alkaline reaction. It is to be neutralized with nitric or chlorhydric acid, and then contains the sodium salt — usually acid — of one or another acid of the series. As the sodium salts do not as a rule crys- tallize as well as those of potassium, I have sometimes found it advan- tageous to add a solution of potassic bromide or nitrate, when, after some hours, crystals of a potassic salt usually separate in abundance, often in fine colorless and transparent crystals. If a large excess of acid is added at once to the mixed solution of sodic tungstate OF ARTS AND SCIENCES. Ill and phosphate, an acid sodium salt is often precipitated immediately, and almost always after standing a day or two. But it must be re- marked that in this case the proportion of tungstic and phosphoric oxides is not always that which existed in the original mixture. In some cases I have fused the tungstate and phosphate together in definite proportions in a large platinum crucible, but this method does not present any special advantage. In other cases I have dissolved tungstic oxide in solutions of alkaline phosphates. Finally, I have in a few instances employed the original method of Scheibler. The alkaline phospho-tungstates, when nob too highly acid, are usually rather easily soluble in water, but in the act of solution they almost always undergo a certain amount of decomposition, a white crystal- line powder being formed which is comparatively insoluble. Some- times the solution becomes milky at once, and remains so for a very long time. In all cases it must be allowed to stand until it becomes perfectly clear, and then poured upon the filter without disturbing the precipitate, as the filtrate would otherwise be turbid. The alkaline phospho-tungstates are not decomposed by hydric sul- phide except to a very limited extent. A current of the gas usually produces a blue color from the reduction of a small portion of the tungstic teroxide to the lower oxide W205. When an alkaline sulphide is added to a solution of a phospho-tungstate a similar reduc- tion is produced. The addition of chlorhydric acid then gives only a small precipitate of tungstic sulphide. Zinc readily reduces a portion of the teroxide to the blue oxide, but the reduction even after some time is very far from complete. The relations of acid phospho-tung- states to salts of the various alkaloids have already been pointed out by Scheibler. In almost all cases nearly insoluble more or less dis- tinctly crystalline precipitates are formed. I find that a beautiful heavy white crystalline salt is thrown down when an acid phospho-tungstate, as, for example, the sodium salt 24 W03 . P206 . 2 Na20 . 4 H20, is mixed with a solution of urea, or even with urine. In this last case the precipitate contains also slightly soluble salts of potassium and ammonium. It is possible that the reaction may be utilized in animal chemistry. The phospho-tungstates also precipitate egg-albumen as a white flocky substance, which may prove to be a definite salt, in which case the high molecular weight of the acid would be of great value in determining the equivalent of the compound. I have made no experiments in this direction, and throw out the suggestion for what it may be worth. Mercurous nitrate precipitates all the phospho-tungstates almost 112 PROCEEDINGS OP THE AMERICAN ACADEMY completely. The yellow precipitate formed becomes more dense and compact by boiling with the supernatant liquid. It is nearly insoluble in pure water, but dissolves to some extent even in very dilute nitric acid. Dilute chlorhydric acid decomposes the salt, phospho-tungstic acid being set free. The mercurous salts of the series are the only ones which are sufficiently insoluble to be available in analysis. Soluble salts 'of the different series of phospho-tungstates usually possess a strongly marked bitter taste. In a single instance the taste is at once sweet and astringent. The salts which are acid in constitu- tion exhibit a strongly marked acid reaction. Analytical Methods. — To determine the sum of the percentages of tungstic and phosphoric oxides the salt was dissolved in water or dilute nitric acid, and the two oxides precipitated together by means of mercurous nitrate with the addition of mercuric oxide, as in the estimation of tungstic oxide in the alkaline tungstates already de- scribed. This method gives good results only when used with great care, as my assistant, Dr. Gooch, observed that the high temperature and long-continued heat required to expel the whole of the mercury also drove off phosphoric oxide, so that the results frequently varied very materially, and were almost always too low. I have sometimes preferred to precipitate the two oxides with mercurous nitrate in small excess from the boiling solution, — as in the case of the tung- states,— and then to evaporate to perfect dryness on a water-bath, continuing the heat until the whole of the free nitric acid was ex- pelled. The dry mass of mercurous phospho-tungstate and basic nitrate adheres somewhat to the evaporating dish, but not so as to render its removal very difficult. Dr. Gooch found that the adhesion was almost entirely prevented by first evaporating the solution and precipitate to a small volume, and then adding water in considerable quantity and evaporating again, this time to perfect dryness. No phosphoric oxide is vaporized on ignition for an hour at a cherry-red heat, and it is not usually necessary to ignite the mixed oxides a second time so as to insure a constant weight, though it is always better to do so. The yellow powder remaining after ignition is a mixture of tungstic oxide, W08, and phosphoric oxide, P205, from which water removes a portion, but not the whole, of the latter. The quantitative determination of the sum of the two oxides by this method is very nearly, but not abso- lutely, accurate. A trace of phosphoric acid almost always remains in the filtrate from the mercurous salt, and may be detected by evap- orating this to dryness, expelling the mercurous oxide by heat, and then igniting a portion of the residue with magnesium wire. The OP ARTS AND SCIENCES. 113 loss of phosphoric oxide is, however, extremely small, and probably never exceeds two or three hundredths of oue per cent. The tungstic oxide was always determined by subtracting the phosphoric oxide as directly determined from the sum of the two oxides. My various attempts to determine the two oxides together by precipitation with salts of lead or barium, after neutralization with an alkali, proved failures in all cases. The precise quantitative separation and estimation of phosphoric oxide in the phospho-tungstates is a matter of no small difficulty. After many trials of various methods, the separation by means of magnesia-mixture was found to give the best results, magnesic chloride being employed. Only, in all cases in which this method is used, it is necessary to redissolve the ammonio-magnesic phosphate first precipi- tated, and to precipitate the salt a second time with ammonia. The whole subject was specially investigated by Dr. F. A. Gooch, and I shall do him and the process the fullest justice by referring to his paper in Volume XV. of these Proceedings. Since the publication of Dr. Gooch's paper, I have also used in many cases the following proc- ess, which gives excellent results. The phosphoric oxide is to be precipitated in the usual manner as ammonio-magnesic phosphate, and well washed with magnesia-mixture and ammonia. The precipitate is to be redissolved in chlorhydric acid, ammonia added in small excess, and afterwards acetic acid, until the reaction is faintly but distinctly acid. The phosphoric oxide is then to be precipitated from the last solution by uranio-sodic acetate in excess. The precipitate must be allowed to settle completely, and the clear supernatant liquid poured upon the filter without disturbing the precipitate. A moderately strong solu- tion of ammonic nitrate is then to be added, and the precipitate again allowed to settle. After repeating this process two or three times, the precipitate may be brought upon the filter and washed with solu- tion of ammonic nitrate. In this manner there is no danger of obtain- ing a turbid or milky filtrate. After drying, the precipitate is to be ignited, moistened if necessary with nitric acid, and again ignited. This process is somewhat longer than that by double precipitation and estimation as magnesic pyrophosphate, but is, I think, rather more accurate. In almost all the analyses, by either method, the filtration and washing of the precipitate was effected by means of the asbestos filters devised by Dr. Gooch* It is hardly possible to speak too highly of this admirable Contrivance, which in a very large number of * Proceedings of American Academy, Vol. XIII. p. 342. vol. xvi. (n. s. viii.J S 114 PROCEEDINGS OF THE AMERICAN ACADEMY cases is to be preferred to any other mode of filtering, and which has been in daily use in my laboratory for nearly two years, with scarcely a single instance of failure. Iu many of the earlier analyses the phos- phoric oxide was precipitated as ammonio-magnesic phosphate after the addition of citric acid in quantity about equal ta the weight of salt taken. Dr. Gooch's later experiments showed that this method gave results which were about Hc/0 too high when the precipitate — as was always the case — was not redissolved and thrown down a second time. In some cases I have applied this determination as a correction to the direct result of the analysis. As in the analyses of the alkaline tungstates, I have usually deter- mined the alkali by difference, making direct estimations only in doubt- ful cases. Ammonia was always expelled by boiling the salt with sodic hydrate, collecting in chlorhydric acid, and weighing as ammonic chloride. Baric oxide was also sometimes estimated by difference. When precipitated from a solution of baric phospho-tungstate by sul- phuric acid, the sulphate always contains phosphoric oxide, and the same is true when ammonic carbonate and ammonia are employed. Phospho-tungstates which are insoluble in water may be resolved by fusion with an alkaline carbonate, preferably by the mixed carbonates : C03 KNa. Water is best determined from the loss by ignition, but in some cases I have found it best to ignite with a weighed quantity of borax. Twenty-four Atom Series. Phospho-tungstic Acid. — The acid is most conveniently prepared by decomposing mercurous phospho-tungstate by dilute chlorhydric acid. I have found it best to proceed as follows. To the mixture of 24 molecules of normal sodic tungstate and 2 mole- cules of sodic phosphate in solution, after boiling for some time, dilute nitric acid free from chlorine is to be added until the reaction is quite dis- tinctly acid. The solution is then to be precipitated hot by mercurous nitrate in small excess, and the yellow flocky mercurous salt washed thoroughly by decantation with hot water. Toward the end of the operation a few drops of solution of mercurous nitrate may be added to the water, as the washings are otherwise apt to become milky. After washing, dilute chlorhydric acid is to be added in small quantities at a time until the yellow color disappears, and is replaced by the white of mercurous chloride. It is well to set aside a small quantity of the mer- curous phospho-tungstate. and to add this to the solution of the acid so as to insure the separation of any remaining traces of chlorhydric acid. After complete subsidence the supernatant liquid is to be filtered off clear and then evaporated in vacuo over sulphuric acid. The sirupy OF ARTS AND SCIENCES. 115 faintly violet liquid gives splendid large transparent crystals of phospho- tungstic acid, which are sometimes colorless and sometimes sulphur- yellow. The crystals effloresce with great rapidity, and therefore do not admit of measurement. They appear to be regular octahedra. The solution of the acid is colorless, and has a strongly acid reaction and bitter taste. Of these crystals, — 1.2791 gr. lost on ignition 0.1809 gr. water = 14.14% 1.3005 gr. lost on ignition with fused borax 0.1842 gr. water = 14.16% 1.4151 gr. gave 1.2130 gr. W03 + P205 = 85.72% 1.5416 gr. gave 1.3201 gr. W03 -f- P206 = 85.64% 1.7365 gr. gave 0.0616 gr. P2OrMg2 = 2-2G% PA The analyses lead to the formula 24 WO, . P206 . 6 H30 -f 47 aq, or WMPa071(HO)12 + 47 a(b which requires : — Calc'd. Mean. 24 WO, 5568 83.55 83.57 83.53 83.61 PA 142 2.13 2.11 2.11 53H80 954 14.32 14.15 14.14 14.16 6664 100.00 99.83 As the phosphoric oxide in the analysis was determined after a single precipitation, a correction of 0.15 is applied to the direct result of the analysis. The crystals had slightly effloresced in drying, which explains the deficiency in the water. A quantity of the 18-atom potassium salt 18 W03 . P205 . 6 K.,0 -f- 26 aq was dissolved and precipitated by mercurous nitrate. The mer- curous salt was then decomposed by dilute chlorhydric acid, and the solution of phospho-tungstic acid obtained evaporated in a flask at about 50° C. by means of a water air-pump, and then allowed to stand in a partial vacuum over sulphuric acid. After some days splendid col- orless crystals formed, which appeared to be octahedra, but which on standing became columnar in structure, opaque, and yellow. The analyses of these crystals corresponded very closely to the formula 24 W03 . P206 . 6 H20 + 34 aq, or W^O^HO),, + 34 aq, as the following analyses show : — 1.4482 gr. lost on ignition 0.1636 gr. water = 11.30% and gave 0.0492 gr. P2OJVlg2 = 2.17% P206 1.5109 gr. lost on ignition 0.1708 gr. water = 11.31% and gave 0.0521 gr. P207Mg2 = 2.20% P205 116 PROCEEDINGS OP THE AMERICAN ACADEMY Caic'd. 24W03 5568 86.59 86.50 86.53 PA 142 2.20 2.20 2.17 40H2O 720 6430 11.21 100.00 11.30 11.31 The yellow columnar mass, after re-solution and standing over sul- phuric acid in pleno gave perfectly colorless regular octahedra, which corresponded to the formula, 24W03 . P205 . 6 H20 + 55 aq, or W24P2On (HO)12 -f- 55 aq. 24W03 5568 Caic'd. 81.78 81.75 81.76 PA 142 2.08 2.14 2.15 61H,0 1098 6808 16.14 100.00 16.11 16.09 In the cases of the two last-mentioned hydrates of the acid, the phosphoric oxide was determined by two successive precipitations as ammonio-magnesic phosphate. The analyses leave no doubt as to the constitution of the acid. Scheibler obtained two different phospho- tungstic acids, to which he gave respectively the provisional formulas H16PWnO« -[- 18 H20, and HnPW10O88 + 8 H20. I should double these and write 22 W03 . P205 . 6 H20 -f 45 aq, or W22P2Oe5(HO)I2 + 45 aq. 20 W03 . P205 . 6 H20 + 21 aq, or W^P.O^HO)^ -f 21 aq. I have not obtained the acid of the 20-atom series, though I shall show further on that there is at least one well-defined salt in which the ratio of tungstic to phosphoric oxide is as 20 to 1. Scheibler does not give the method which he employed for the separation of the two oxides, and I consider it at least probable that his acid 22 WOa . P205 . 6 H20 -f 45 aq is identical with the first of the three hydrates which I have described above. The solution of phospho-tungstic acid forms a colorless heavy oily liquid, with a high refracting power. It has an acid as well as bitter taste, and readily expels carbonic dioxide from carbonates. On stand- ing for some days, the solution undergoes partial decomposition with deposition of a white crystalline powder. This powder is also almost always deposited, in greater or less quantity, in the preparation of the OP ARTS AND SCIENCES. 117 acid, but I could not obtain it in a state of purity sufficient for analysis. It may be worth while to note as a possible source of differ- ence, that Scheibler obtained his acids by the decomposition of the cor- responding barium salts by dilute sulphuric acid. The method of preparation which I employed is, I think, preferable. 24 : 2 Acid Sodic Phospho-tungstate. — When chlorhydric or nitric acid is added in large excess to a solution of normal sodic tungstate, and of hydrodisodic phosphate containing 24 molecules of the former to 2 of the latter, a salt is obtained which is usually colorless when chlorhydric acid is employed, and pale sulphur yellow when nitric acid is used. This salt crystallizes more easily than the other salts of sodium. According to Dr. Gooch, the small granular crystals appear to be either monoclinic or triclinic. They are readily soluble in water, but invariably undergo a slight decomposition in the act of solution, a small quantity of a white crystalline powder being formed which is in- soluble, or but slightly soluble. The yellow and the colorless crystals have the same crystalline form and the same reactions. Their consti- tution is also the same, as the following analyses show : — I. 1.4900 gr. lost on ignition 0.1107 gr. water = 7.43% 1.1100 gr. gave 1.0016 gr. W08 -f PA = 90.23% 1.8072 gr. " 0.0679 gr. PaOTMg8 = 2A0% P20* II. 0.9913 gr. lost on ignition 0.1809 gr. water = 7.34% 0.8945 gr. " " 0.0658 gr. " = 7.32% 1.0745 gr. gave 0.9698 gr. W03 -f- PA = 90.26% 1.1508 gr. " 0.0420 gr. P2OrMg2 = 2.33% P206 III. 1.4933 gr. lost on ignition 0.1115 gr. water = 7.47% 1.3273 gr. gave 1.5424 gr. « 1.2990 gr. " 1.1503 gr. " 1.1969 gr. WOs + PA 1.3920 gr. " 0.0470 gr. P207Mg2 0.0428 gr. " IV. = 90.18% == 90.25% = 2.31% PA = 2.38% " 1.8027 gr. lost on 1.1559 gr. " ignition 0.1349 gr. water " 0.0860 gr. " = 7.48% = 7.44% 1.1269 gr. gave 0.9624 gr. " 0.6787 gr. « 1.0151 gr. W03 + PA 0.0367 gr. P207Mg2 0.0263 gr. = 90.08% = 2.44% PA = 2.48% " 118 PROCEEDINGS OF THE AMERICAN ACADEMY Analyses I. and II. were made with two different preparations of the colorless crystals ; III. and IV. were made with the sulphur-yellow salt. The determinations of (W03 -\- P20.) in I., II., aud III. were made by the evaporation process without the use of mercuric oxide, but in IV. the oxide was employed. As a check upon the quantity of sodic oxide two direct determinations were made in III. the oxide being weighed as nitrate. In this manner, 1.3273 gr. gave 0.0875 gr. N03Na = 2.40% 1.2593 gr. " 0.0924 gr. " = 2.68% Na20 The mean of these two is 2.54%. As the phosphoric oxide in the analyses above cited was determined from a single precipitation as ammonio-magnesian phosphate, I have, as usual in such cases, applied a correction of 0.15% to the mean. These analyses lead to the formula 24 W03 . P205 . 2 Na20 . 4 H20 -f 23 aq, or, W24P2071(NaO)4(HO)8 + 23 aq. 24 W03 5568 P205 142 2 Na20 124 Calc'd. Mean. 88.10 88.04 87.98 2.25 2.24 2.25 1.97 2.27 . . . 88.08 88.02 2.18 2.16 88.02 2.13 88.09 2.29 2.33 27 H20 486 7.68 7.49 7.43 7.32 7.34 7.47 7.50 7.48 7.44 6320 100.00 The mean of the five determinations of (WO, -f- P20.) is 90.20. The formula requires 90.35. There can, I think, be no reasonable doubt as to the constitution of the acid sodium salt, though it is difficult to obtain it in a state of absolute purity. The salt is very conveniently prepared, however, and makes an excellent reagent for alkaloids. For this special purpose it is best to mix the normal tungstate and hydrodisodic phosphate in the proportion of 24 atoms of the former to 3 or 4 of the latter, boil the mixed solutions for a short time, filter, and add chlorhydric acid in excess, but in small successive portions. A precipitate is usually formed on each addition of acid which disappears on stirring the liquid. On standing, a mass of crystals of the acid suit separates. This should be drained, washed with a little cold water, then dissolved in cold water for a reagent, the clear liquid only being used. The 24 : 2 acid phospho-tungstate of sodium appears to be always formed when an excess of chlorhydric or nitric acid is added to a so- OP ARTS AND SCIENCES. 119 lution containing sodic tungstate and phosphate, in which the propor- tion of the latter to that of the former is as 1 to 12, or as 1 to any number less than 12. In other words, it appears to be the limiting term of all the series. When the salt is fused with sodic carbonate, carbonic dioxide is given off, but not in the proportion which might be expected. In one experiment, 2.2298 gr. lost 0.5408 gr. CO., and H20 = 16.94% 1.2621 gr. lost on simple ignition 0.0922 gr. H20 = 7.31% The ratio of the W03 in the salt to the C02 expelled is here as 38 : 22, or very nearly as 24 : 13. If the ratio were as 24 : 13, the reaction would be represented by the equation 24 W03 . P205 . 2 Na20 -j- 13 C03Na2 = 12 (2 W03 . Na20) + P205 . 3 Na20. A small proportion of neutral tungstate, W04Na2, is probably formed by the further action of the acid tungstate on the alkaline car- bonate. The 24 : 2 acid sodium salt gives no precipitate with the sulphates of zinc, manganese, and copper; a white crystalline precipitate with argentic nitrate, and after a short time with baric chloride and amnio- nic nitrate ; no precipitates with calcic and strontic chlorides, but after a short time scanty crystalline salts. The 24 : 2 acid salt is the only sodium compound of the 24-atom series which I have been able to prepare. When a solution of this salt is carefully neutralized with sodic carbonate, the 6-atom or fully saturated salt, 24 W03 . P205 . 6 Na20, possibly exists in the solu- tion, but a definite salt could not be obtained by evaporation. When neutral sodic tungstate and hydrodisodic phosphate are mixed in the proportion of 24 : 2, and acetic acid is added to the solution after boiling for some time, no precipitate is formed, but alcohol throws down a colorless oil which soon solidifies to a white gummy mass. I did not obtain a crystalline well-defined salt from this by re-solution and evaporation, but others may perhaps be more successful. When a sufficient quantity of sodic carbonate is added to a solution of the acid sodic phospho-tungstate, a mixture of sodic tungstate and sodic phosphate appears to be formed. 24 W03 . P2Os . 2 Na20 + 25 C03Na2 = 24 (W03 . Na20) + P205 . 3 Na20. The phospho-tungstate is formed again on adding an excess of acid. 120 PROCEEDINGS OP THE AMERICAN ACADEMY 24 : 3 Acid Potassium Salt. — When a solution of the 24 : 2 acid sodic salt is added to one of a salt of potassium, a heavy white crystal- line very slightly soluble precipitate is formed, either immediately or after a short time. The salt forms very small granular crystals. It requires a large quantity of water for solution, a white much more insoluble salt being formed in small quantity by the action of water, so that the liquid is, and for a long time remains, milky. It is best, therefore, simply to wash the precipitate with cold water until this begins to give a turbid filtrate, and then to dry the salt by pressure with woollen paper. The salt is also formed when chlorhydric or nitric acid is added to a solution of potassic phosphate and tungstate in the proportion of 2 molecules of the former to 24 molecules of the latter, — the two solutions being previously boiled together for some time in a platinum vessel. The reaction in this latter case may be expressed by the equation 24 W04K2 + 2 P04KH2 -4- 44 HC1 === 24 W03 . P205 . 3 K20 -f "44 KC1 -4- 24 aq, and in the case of precipitation by the acid sodium salt, by the equation 24 AVO3 . P80. . 2 Na20 . 4 H,0 + 6 KN03 = 24 W03 . P205 . 3 K20 . * 3 H20 4- 4 NaN08 + 2 N08H + 3H20. In this salt, — 1.1478 gr. gave 1.0588 gr. WO, -f P206 =92.25% 1.1764 gr. " 0.0468 gr. P2OrMg2 = 2.54% P206 1.7383 gr. lost on ignition 0.0576 gr. water = 3.31% 1.7638 gr. " " 0.0578 gr. " = 3.28% The analyses lead to the formula 24 W03 . P205 . 3 K20 . 3 H20 -f 8 aq. Calc'd. Mean. 24 W03 5568 89.93 89.86 89.86 PA 142 2.29 2.39 2.39 corrected. 3 K,0 283 4.57 4.45 11 H20 198 3.19 3.30 6191 100.00 100.00 3.28 3.31 n another preparation of the same salt, — 0.7340 gr. gave 0.6660 gr. W03 -f P20. = 90.74$ 1.1400 gr. " 1.0317 gr. " • = 90.50% 0.8028 gr. " 0.0310 gr. P207Mg2 = 2.47% P206 1.5568 gr. lost on ignition 0.0805 gr. water = 5.17% 0.8822 gr. " " 0.0455 gr. " == 5.16% OF ARTS AND SCIENCES. 121 The analyses correspond to the formula 24 W03 . P205 . 3 K20 . 3 H20 + 14 aq. ,18 5.17 24W03 5568 .Calc'd. 88.38 Mean. 88.30 88.42 PA 142 2.26 2.32 2.32 3K20 283 4.49 4.21 17H20 306 4.87 5.17 5.16 6299 100.00 100.00 24 : 3 Acid Ammonium Salt. — When a solution of a salt of am- monium is mixed with one of sodic tungstate and phosphate, no precipi- tate is formed, even after standing ; but if a large excess of chlorhydric or nitric acid is poured in, a white or very pale yellowish heavy crys- talline salt is thrown down in large quantity. This salt is an acid phospho-tungstate of ammonia, the constitution of which varies with the proportions of the salts employed in its preparation and with the conditions of the experiment. The different salts, however, resemble each other very closely, and may be described in the same terms. They are either perfectly white or have in mass a faint tinge of yellow and an extremely fine-grained crystalline structure. They are very slightly soluble even in hot water, and give milky emulsions which settle very slowly. Like many other phospho-tungstates and tungstates, they are difficult to wash, as they pass through the closest filter-paper with extraordinary facility. This difficulty may, however, be overcome by adding ammonic nitrate to the wash-water. The acid phospho-tungstates of ammonium are soluble in ammonia-water, but the crystals obtained from such solutions are either ammonic tungstates or salts of series different from that to which the salt dissolved belonged. They are readily decomposed by a red heat, leaving a mixture of tungstic and phosphoric oxides. When boiled with mercurous nitrate, they yield mercurous salts and ammonic nitrate. In one preparation in which sodic tungstate and phosphate were mixed in the proportion of 20 atoms of the former to 2 of the latter, ammonic nitrate was added, and afterward nitric acid. The precipitate was washed with solution of ammonic nitrate, and after- ward with alcohol and water, and dried by pressure with woollen paper. Of this salt, — 122 PROCEEDINGS OF THE AMERICAN ACADEMY 1.3460 gr. lost on ignition 0.1405 gr. H20 -f- NIT, = 10.44% 1.6407 gr. lost on ignition 0.1707 gr. H.,0 + NH, = 10.40% 1.2038 gr. gave 0.0430 gr. P2OrMg2 ="2.27% P206 (twice precip.) 1.3960 gr. gave 0.0504 gr. P207Mg2 = 2.31 % " 1.4890 gr. gave 0.0720 gr. NH4Q. = 2.35% (XH4)aO These analyses lead to the formula 24 WO, . P205 . 3 (NH4)20 . 3 H20 -f 26 aq. Calc'd. Mean. 24 WO, 5568 87.17 87.29 87.27 87.31 PA 142 2.22 2.29 2.27 2.31 3 (NH4)20 156 2.44 2.35 2.35 29 H20 522 8.17 8.07 8.05 8.09 6388 100.00 100.00 It will be observed that in this case the 24-atom salt was obtained under conditions which a priori should have yielded a 20-atom salt. I have already stated that salts of urea are precipitated from their solu- tions by acid sodic phospho-tungstate 24 W03 . P2Os . 2 Na20 . 4 H20. The precipitation is, however, not complete, and the process does not appear to be available as a method of analysis. "When phosphate of aniline and 10 : 4 sodic tungstate are dissolved together, and the solution is boiled for a short time, chlorhydric acid gives an abundant yellowish-white precipitate. On re-solution the precipitate yields pale sulphur-yellow crystals, which are readily solu- ble in alcohol. Phosphate of para-toluidin behaves in a similar man- ner; the phospho-tungstate formed is readily soluble, and crystallizes in long yellow silky needles. I did not succeed in making the insolubility of the acid ammonic phospho-tungstate available in analysis, either for the determination of ammonia or for that of phosphoric acid. For the last-named esti- mation the phospho-molybdates appear to be far better adapted. 24 : 3 Acid Barium Salt. — When 10:4 sodic tungstate is dissolved and a small quantity of phosphoric acid is added, the hot solution gives with baric chloride a heavy white flocky precipitate, which readily dis- solves in hot dilute chlorhydric acid. The solution, after filtration from a small quantity of flocky matter, is pale yellow, and after some time deposits splendid nearly colorless crystals, which appear to be octahe- dra. These are readily soluble in hot water without decomposition, and may be repeatedly recrystallized without difficulty. Of these crystals. — or, OF ARTS AND SCIENCES. 123 0.7672 gr. gave 0.6278 gr. W03 -f P208 = 81.83% 1.5557 gr. lost on ignition 0.1872 gr. water = 12.03% 1.3732 gr. lost on ignition 0.1641 gr. water = 11.95% 1.6196 gr. gave 0.1547 gr. S04Ba = 6.27% BaO and 0.0581 gr. P207Mg2 = 2.29% P205 1.2094 gr. gave 0.1158 gr. S04Ba = 6.28% BaO The analyses agree fairly well with the formula 24 W03 . P20. . 3 BaO . 3 H20 + 43 aq, W24P2On(Ba02)3(HO)G + 43aq. The same salt is formed when two atoms of 12 : 5 sodic tungstate are boiled for a time with two atoms of sodic phosphate and chlorhydric acid is added in excess. Baric chloride then gives after a time crys- tals exactly similar to those described above. In a salt prepared in this manner, — 1.0020 gr. gave 0.8173 gr. W08 + P206 = 81.56% 1.4718 gr. gave 0.1648 gr. S04Ba = 6.97% BaO and 0.0518 gr. P207Mg2 = 2.25% P2Os 1.4841 gr. lost on ignitioa 0.1717 gr. water = 11.57% Calc'd. Mean. 24WOs 5568 79.57 79.57 79.69 79.46 P205 142 2.03 2.12 2.14 2.10 3 BaO 459 6.56 6.62 "§h 6.28 6.97 46 H20 828 11.84 11.78 12.03 11.95 11.57 #6977 100.00 100.09 The phosphoric oxide determinations are corrected in both analyses. The percentage of baric oxide as determined by difference, which is the more accurate method, is 6.53. The salt effloresces with extraordi- nary rapidity, so that it is very difficult to dry it for analysis by pres- sure between folds of woollen paper. Twenty-two Atom Series. — The phospho-tungstates containing 22 atoms of tungstic oxide to 1 of phosphoric oxide are represented by apparently well-defined salts of potassium, sodium, and ammonium. I have not succeeded in preparing the corresponding acid. As already stated, Scheibler has given provisionally the formula Hi8pwi As + 18 H20, or 22W03.P2Os.6H20 + 45aq, 124 PROCEEDINGS OF THE AMERICAN ACADEMY to an acid which he obtained by the decomposition of a salt of barium, and it may be that this is really the acid of the 22-atom series. Further investigations must decide the point. The salts of the 22- atom series closely resemble those of the 24-atoni series already de- scribed, and- are only to be distinguished from them by analysis. 22 : 2 Potassium Salt. — The 18-atom potassium salt, 18 W03 . P205 . 6 K20 + 30 aq, gives with chlorhydric or nitric acid a heavy white fine-granular precip- itate of an acid salt which belongs to the 22-atom series, and which has the formula 22 WOj . P205 . 2 K20 . 4 H20 + 2 aq, as the following analyses show : — 1.5679 gr. lost on ignition 0.0318 gr. water = 2.03% 1.0728 gr. lost on ignition 0.0222 gr. water = 2.07% 1.5061 gr. gave 1.4250 gr.W08 + P206 = 94.61% 1.1873 gr. gave 1.1253 gr.W03+P206 = 94.78% 2.1607 gr. gave 0.0927 gr.P2O.Mg2 = 2.74% P20( 2.2367 gr. gave 0.0950 gr.P2OrMg2 = 2.72% « Calc'd. Mean. 22 WO, 5104 92.08 92.11 92.20" 92.03 PA 142 2.56 2.58 2.59 2.57 com 2 K20 189 3.41 3.26 6 H20 108 1.95 2.05 2.03 2.07 5543 100.00 The salt is very slightly soluble in water. The solution becomes milky, and remains so for a long time. Its formation from the normal 18-atom salt may perhaps be expressed by the equation, 10 (18 W03 . P20.3 . 6 K20) + 84 HC1 + 36 H00 = 9 (22 W03 . Po05 . 2 K20 . 4 H20) + 2 (P206 . 3 K20) + 84 KC1 -f 42 H20. " 22 : 3 Ammonium Salt. — An acid ammonium salt of this series was obtained from a mixture of sodic tungstate and phosphate, to which amnionic nitrate and excess of chlorhydric acid had been added exactly as in the preparation of the 24-atom salt already described. The salt was in very small colorless granular crystals, slightly soluble in cold water, but dissolving to some extent in hot water, giving a milky liquid, settling very slowly. Its other properties are not distinguish- able from those of the 24-atom salt. Of this salt, OP ARTS AND SCIENCES. 125 1.5911 I lost on I 0.1470 0.9086 I ignition I 0.0837 1.0934 J [ 0.1009 J Gr. Gr. Perct. Per ct. 0.8697] [ 0.0805] [ = 9.26 = 90.73 W03-|-P206 water and I = 9.24 = 90.76 " ammonia I =9.21 = 90.79 « 1=9.21 = 90.79 " ( 1.0934 gave 0.0439 P207Mg2 = 2.63 P20. 1.7970 " 0.0993 NH4C1 " = 2.68(NH4)20 These analyses correspond very closely to the formula, 22 W03 . P205 . 3 (NHJ20 . 3 H20 -f 18 aq, which requires : — Calc'd. Mean. 22W03 5104 88.30 88.29 88.25 88.28 88.31 88.31 P205 142 2.46 2.48 2.48 corr .' 3 (NHJ20 156 2.69 2.68 2.68 21H20 _378 6.55 6.60 6.58 6.56 6.53 6.53 5780 100.00 100.05 22 : 2 Sodium Salt. — It has already been mentioned that, in the preparation of the acid sodium salt of the 24-atom series, a white very slightly soluble crystalline powder is formed in greater or less quantity. This salt cannot be recrystallized for analysis, and must therefore be washed with cold water to remove traces of the soluble acid salt. Hot water dissolves it in small proportion only, the solution remaining milky for a long time. In one preparation of this salt, — ( 0.8405 gr. gave 0.7962 gr. W03 + P„05 = 94.73% ( 0.8405 gr. « 0.0330 gr. P2017Mg2 " = 2.51$ {^XdjI^A 1.4990 gr. lost on ignition 0.0403 gr. water = 2.69% These analyses lead to the formula 22 W03 . P205 . 2 Na20 . 4 H20 + 5 aq. Calc'd. 22W08 5104 92.26 92.22 PA 142 2.56 2.51 2Na20 124 2.25 2.58 9 H20 162 2.93 2.69 5532 100.00 22 : 4 Barium Salt. — This salt was obtained by mixing neutral sodic tungstate and hydro-disodic phosphate in the proportion of 24 : 2, neutralizing with acetic acid, and adding a solution of baric chloride. Small sharp prismatic crystals formed after a short time, soluble in hot 126 PROCEEDINGS OP THE AMERICAN ACADEMY water apparently without any decomposition, and separating again from the solution in colorless needles. Of this salt, — 0.6900 gr. gave 0.5494 gr. WO„ -f- P205 = 79.62% 0.6900 gr. " 0.0826 gr. P2OnU2 = 2.34% P205 0.6734 gr. " 0.5372 gr. W03 + P2Os =79.71% 1.5296 gr. " 0.2163 gr. S04Ba = 9.24% BaO 0.9682 gr. lost on ignition 0.1076 gr. water =11.12% 0.7064 gr. " " 0.0787 gr. " = 11.14% These analyses lead to the formula 22 W08 . P205 . 4 BaO . 2 H20 -f 39 aq, W^O^BaO^HO), + 39 aq. 77.28 Calc'd. Mean. 22W03 5104 77.37 77.33 77.37 *A 142 2.15 2.34 2.34 4 BaO 612 9.28 9.24 9.24 41H20 738 11.19 11.13 11.12 6596 100.00 100.04 11.14 The phosphoric oxide was precipitated twice. Twenty Atom Series — The salts of this series closely resemble those which have been described. I did not succeed in preparing the acid, though I made repeated attempts to do so by mixing sodic tungstate and phosphate together in the proportion of 20 molecules of the former to 2 of the latter, neutralizing with nitric acid, precipitating by mercurous nitrate, and decomposing the mercurous salt by dilute chlor- hydric acid. The acid formed always underwent partial decomposition upon concentration, a white crystalline powder being separated while the 24-atom acid was formed. The only well-defined salt of the series which I have obtained is the normal barium compound. From this it will doubtless be possible to obtain others by double decomposition. Nymal 20-atom Barium Suit. — As the baric phospho-tungstates crystallize in general much more readily than the corresponding sodic salts, I employed them to determine what compounds are formed when sodic tungstate and phosphate are mixed in various proportions. To solutions of the two salts in the ratios of 24 molecules of the for- mer to 2 of the latter, of 18 to 2, and of 12 to 2, chlorhydric acid was added until the reaction became just distinctly acid. Baric chloride was then added in excess, and the solutions were quickly filtered from the insoluble white precipitate formed. Beautiful colorless crystals OF ARTS AND SCIENCES. 127 formed, which were readily soluble in hot water, and could be recrystal- lized without difficulty. These salts proved to have in all cases the same composition, and are represented by the formula 20 W05 . P20- . 6 BaO + 48 aq, as the following analyses show : — I. 1.1103 gr. loston ignition with fused borax 0.1458 gr. = 13.14%water. 1.1831 gr. " " " " 0.1560 gr. = 13.18% " 1.0691 gr. gave 0.7775 gr. W03 and P205 = 72.72% 0.9390 gr. " 0.6850 gr. " = 72.84% II. 1.0676 gr. lost on ignition 0.1400 gr. = 13.11 %water. 0.6550 gr. gave 0.4763 gr. W03 and P205 = 72.72% III. 1.1110 gr. lost on ignition 0.1461 gr. = 13.15%water. 0.6409 gr. gave 0.4667 gr. W03 and P2Os = 72.81 % and 0.0704 gr. P2OnU2 = 2.18% P2Os 0.6222 gr. gave 0.0710 gr. P2OnU2 = Analyses I. were made with the salt from the 24 to 2 ; obtained from the 12 to 2 ; and III. from the salt of the ture. The phosphoric oxide was precipitated twice. 70.50 70.62 70.50 13.14 13.18 13.11 13.15 hot water, giving a somewhat milky solution. Chlorhydric acid gives no precipitate at first, but after a time a white crystalline powder is formed, which is the acid salt of the 24-atom series already described. The fact that the same salt is formed independently of the propor- tions of sodic tungstate and phosphate is an important one, and illus- trates the peculiarities of the series of phospho-tungstates which I have already pointed out. -Eighteen Atom Series. — When normal sodic tungstate and hydro- disodic phosphate are dissolved together in the proportion of 20 molecules of the former to 2 of the latter, and acetic acid is added to Calc'd. Mean. 20 W03 4640 70.67 70.55 P203 142 2.17 2.22 6 BaO 918 13.99 14.09 48 H20 864 13.17 13.14 6564 100.00 100.00 The salt diss olves readily in 2.26% " II. from that 18 to 2 mix- 70.59 2.18 2.26 128 PROCEEDINGS OP THE AMERICAN ACADEMY * the boiling solution until a distinctly acid reaction is obtained, alcohol in excess precipitates a white indistinctly crystalline salt. This dis- solves very readily in water, but gives on evaporation a gummy mass, and distinct crystals cannot be obtained. The solution of this salt gives no precipitate at first with salts of potassium, but after a short time beautiful colorless crystals are formed in abundance. The salt dissolves in a rather large excess of water, leaving a small quan- tity of a white insoluble compound. It crystallizes best from a solu- tion which is not very concentrated, and which is allowed to evaporate spontaneously in the air. The crystals obtained in this way are color- less and well-defined prisms. On re-solution it almost always leaves a small quantity of the slightly soluble salt ; but when the whole is dissolved together, the more soluble compound crystallizes without perceptible admixture of the other. From very concentrated solu- tions I obtained a white granular salt, which, on re-solution in a rather large quantity of water, gave the colorless crystals again. Of the colorless transparent crystals, — 1.1470 gr. gave 0.9372 gr. WO, -f P20. = 81.71% 1.5149 gr. " 1.2387 gr. « 1.3494 gr. lost 0.1089 gr. water 1.5806 gr, " 0.1277 gr. " 1.1391 gr. gave 0.0498 gr. Mg.,P20. 1.1856 gr. " 0.0506 gr. " 1.5149 gr. " 0.4738 gr. AgCl These analyses correspond to the formula 18 W03 . P205 . 6 K20 -f 23 aq = 81.77% 8.07% 8.08% = 2.80% P205 2.93% " = 10.26% potassium. which requires ■ — CalcM. Mean . 18W08 4176 78.81 79.12 78.95 79.01 PA 142 2.68 2.62 2.65 2.58 6K20 566.4 10.69 10.24 31H20 414 7.82 8.08 8.07 8.08 5298.4 100.00 Of the white granular hydrate, — 1.3868 gr. gave 1.0985 gr. W03 -j- P205 = 79.21% 0.9528 gr. " 0.7556 gr. " = 79.30% 1.0396 gr. « 0.0409 gr. P20,Mg2 = 2.57% P2Os 1.0614 gr. " 0.0425 gr. " = 2.56% " 1.0102 gr. lost on ignition 0.1009 gr. water = 9.99% 1.7974 gr. « " 0.1800 gr. " =10.01% OP ARTS AND SCIENCES. 129 The corresponding formula is 18 W03 . P205 . 6 K20 + 30 aq, which requires — Calc'd. Mean. 18 W03 4176 76.98 76.84 76.89 76.80 PA 142 2.62 2.42 2.41 2.42 6K20 566.4 10.44 10.74 30H2O 540 9.96 10.00 9.99 10.01 5424.4 100.00 The prismatic and granular salts, therefore, only differ in water of crystallization. It must be remarked, however, that the corrected percentages of the phosphoric oxide in the analyses of the granular salt are too low, which is unusual. 18:1 Acid Potassium Salt. — When the normal salt is dissolved in water and chlorhydric acid is added in excess, a White crystalline precipitate is formed, which is but very sparingly soluble in water. Of this salt,— 1.2955 gr. gave 1.1828 gr. W03 + P2Os = 91.30% 1.3200 gr. " 1.1994 gr. " =90.86% 1.1390 gr. « 0.0592 gr. P2OrMg2 = 3.32% P205 1.5900 gr. " 0.0817 gr. " = 3.29% " 1.5225 gr. lost on ignition 0.1087 gr. water == 7.14% 1.1966 gr. " " 0.0856 gr. " = 7.16% These analyses corrrespond to the formula 18 WG3 . P2Os . K,0 . 5 H20 + 14 aq. Calc'd. Mean. 18 W03 4176 87.84 87.93 88.15 87.71 P206 142 2.99 3.15 3.17 3.14 corrected. K.,0 94.4 1.98 1.77 19 H20 342 7.19 7.15 7.16 7.14 4754.4 100.00 100.00 Ammonium Salt. — The ammonium salt of the 18 atom series may be prepared in the manner given above for the normal potassic com- pound. When amnionic acetate and alcohol are mixed with a concen- trated solution of the sodium salt, no precipitate is formed at first, but after some hours a mass of white crystals is thrown down. After washing with alcohol and re-solution, crystals may sometimes be ob- tained, but the salt usually forms a nearly colorless gummy mass. In this case white opaque crystals separate from a thick and sirupy vol. xvi. (n. s. viii.) 9 130 PROCEEDINGS OF THE AMERICAN ACADEMY mother liquor. The crystals are soft and gummy to the touch. I did not succeed in obtaining the salt in a state of purity suitable for analysis. Sixteen Atom Series. — The only representatives of this series which I have obtained are salts of calcium, potassium, and ammonium. They are all well defined and more or less distinctly crystalline. 16:1 Acid Calcium Salt. — When calcic tungstate, W04Ca, is boiled with a pure dilute solution of phosphoric acid, the salt is dissolved very slowly ; but on addition of a few drops of chlorhydric acid, the tungstate passes quickly into solution. The liquid deposits on evap- oration colorless flat tabular crystals readily soluble in water. Of these crystals, — 0.7356 gr. gave 0.6992 gr. W03 + P205 = 95.05% 0.7356 gr. " 0.0390 gr. P2O.Mga = 3.39% P205 1.0347 gr. lost on ignition 0.0366 gr. water = 3.54% The phosphoric acid was twice precipitated. The analyses lead to the formula 16 W03 . P205 . CaO . 5 H20 + 3 aq, which requires : — Calc'd. 16 WOs 3712 91.56 91.66 PA 142 3.50 3.39 CaO 56 1.38 1.41 (diff.) 8H20 144 3.56 3.54 4054 100.00 16:4 Acid Potassium Salt. — - In the attemp t to prepare the s salt to which Scheibler gave provisionally the formula Na5HuW6P,031 -J- .13 aq, I obtained a thick sirupy liquid, which on dilution with water gave with potassic bromide, after standing a few hours, beautiful colorless needles. The salt is readily soluble in hot water. After recrystalli- zation, — 0.5991 gr. gave 0.5000 gr. WO, -4- P205 = 83.46% 2.1547 gr. " 0.1005 gr. P207Mg2 " = 2.98% P2Os 1.0492 gr. lost on ignition 0.0841 gr. water = 8.01% The analyses give the formula 16 W03 . P205 . 4 K20 . 2 H20 -f- 19 aq, or, W16P2047(KO)s(HO)4+19aq, OP ARTS AND SCIENCES. 131 iich requires : — Calc'd. 16 W03 3712 80.53 80.48 PA 142 3.08 2.98 4K,0 377.6 8.19 8.53 (diff.) 21 H20 378 8.20 8.01 4609.6 100.00 16:6 Ammonium Salt. — This beautiful salt was prepared by- adding a solution of amnionic chloride to the sirupy liquid obtained by boiling 12:5 sodic tungstate with half its weight of a strong solution of pure phosphoric acid. After standing twelve hours an abundant precipitate of the ammonium salt was formed. This precipi- tate, after being well drained and twice recrystallized, gave very fine flat prismatic crystals. It is the best-defined ammonium salt which I have obtained. The salt is readily soluble in hot water, and crystal- lizes as the solution cools. Of this salt, — 1.4108 gr. lost on ignition 0.1627 gr. H.20 + NH3 = 11.58% < 0.7705 gr. " " 0.0886 gr. " =11.49% 1 0.7705 gr. gave 0.1243 gr. P.2OnU2 = 3.21% P205 0.9629 gr. " 0.1430 gr. NH4C1 = 7.17% (NH4)20 The analyses correspond with the formula 16 W03 . P205 . 6 (Nig20 -f 10 aq, which requires : — Calc'd. Mean. 16 W03 3712 85.41 85.28 85.30 85.26 P205 142 3.27 3.21 3.21 6 (NH4)20 312 7.18 7.17 7.17 10 H20 180 4.14 4.34 4.32 4.36 4346 100.00 100.00 Fourteen to Two Series. — The only compound of this series which I have obtained is a sodium salt with the empirical formula 14 W03 . 2 PA • 5 Na20 -f 42 aq. I regard this as a double salt, or perhaps as a compound of an 8-atom and a 6-atom salt. 14:5 Sodium Salt. — In the communication already referred to,* Scheibler described briefly a sodium salt to which he gave provision- ally the formula Na5HnPMi + 13 H20. * Berichte der Deutschen Chemischen Gesellschaft, V. 801. 132 PROCEEDINGS OF THE AMERICAN ACADEMY This salt was obtained by boiling 12 : 5 sodic tungstate with half its weight of phosphoric acid. After a short time the salt separates in beautiful crystals. As Scheibler's salt evidently belongs to a 6-atom series, and has therefore a special theoretical interest, I endeavored in various ways to prepare it, but in all cases without success. By boil- ing 12 : 5 sodic tungstate with half its weight of phosphoric acid I ob- tained a thick sirupy liquid, wbich after long standing gave crystals. In another experiment about 75 gr. of the sodium salt were boiled with 13 gr. of sirupy pure phosphoric acid. After dilution and standing for some days, splendid colorless prismatic crystals separated, identical in appearance with those of the last experiment. These were redis- solved and recrystallized several times. Of this salt, — 0.5551 gr. gave 0.4272 gr. W03 + P205 = 76.95% 0.5787 gr. " 0.4459 gr. " = 77.06% 1.5430 gr. " 1.1884 gr. " =77.02% 1.0058 gr. « 0.0980 gr. P207Mg2 = 6.35% P206 1.0285 gr. " 0.1014 gr. " = 6.34% " 1.0023 gr. " 0.3214 gr. P2OnU2 = 6.38% " 1.0152 gr. lost on ignition 0.1656 gr. water == 16.31% 1.0240 gr. " " 0.1677 gr. " =16.37% 0.9922 gr. " " 0.1612 gr. " = 16.24% These analyses correspond fairly well to the formula 14 W08 . 2 P204 . 5 Na20 -f- 42 aq, which requires : — Calc'd. Mean. 14 W03 3248 70.64 70.65 70.59 70.70 70.66 2 PA 284 6.18 6.36 6.35 6.34 6.38 5 Na20 310 6.74 6.65 ... 42 H20 756 4598 16.44 100.00 16.34 16.31 16.37 16.34 The phosphoric oxide, which was twice precipitated, is too high, but it may be that in such salts a third precipitation is necessary to effect a perfect separation. I should write the formula of the salt, provisionally, either, , 6 W03 . P2Os . 3 Na20 . 3 H20 + 8 W03 . P205 . 2 Na20 . 4 H20 -f- 35 aq, or, 6 W03 . P205 . 2 Na20 . 4 H20 + 8 W03 . P206 . 3 Na20 . 3 H20 + 35 aq. There appears to be no reason for distributing the sodic oxide in one way rather than in the other. On the other hand, it is perhaps equally OP ARTS AND SCIENCES. 133 probable that the salt is a compound of two acid salts of a 7-atom series, and that its formula is 7 W03 . P205 . 3 Na20 . 3 H20 -f 7 W03 . P205 . 2 Na20 . 4 H20 + 35 aq. Among the corresponding phospho-molybdates there is at least one series in which the number of atoms of the teroxide is odd. Po- tassium and ammonium salts in this series have respectively the formulas 5 M0O3 . P203 . 3 K20 . 3 H20 + 4 aq, 5 M0O3 . P205 . 3 (NH4)20 . 3 H20 + 4 aq, if, provisionally, we consider the acid as 12-basic. "With respect to the formula given above, and which is that of an acid double salt, I may remark that I shall describe farther on a salt of the 5-atom molybdenum series with the formula 5 M0O3 . P205 . 3 (NH4)20 . 3 H20 + 5 MoOs . P205 . 2 (NH4)20 . 4 H20, and that Rammelsberg has already described the corresponding potas- sium compound. From the general analogy between tungsten and molybdenum, the existence of phospho-tungstates with an uneven number of atoms of tungstic oxide may be fairly inferred from that of phospho-molybdates of the type of the 5-atom compounds above mentioned. I must leave the question undecided, for the present at least, as I have not succeeded in obtaining corresponding salts of potassium, ammonium, strontium, or calcium. The salt crystallizes in long, flat prismatic forms, and appears to be perfectly homogeneous, so that I believe it should be regarded as a definite compound, and not as a mixture. It is very soluble in water, and crystallizes only from sirupy solutions. It has a strongly marked sweet taste, which is at the same time astringent and very slightly bitter. The solution of the sodium salt gives with potassic bromide a beautiful crystalline precipitate, already described, and having the formula 16 W08 . P205 . 4 K20 . 2 H20 + 19 aq, and with ammonic chloride, the ammonium salt 16 W03 . P205 . 6 (NH4)20 + 10 aq, also noticed above. I endeavored to obtain the normal 6-atom sodium salt 6 W08 . P205 . 6 Na20 by boiling six atoms of neutral sodic tungstate with 134 PROCEEDINGS OP THE AMERICAN ACADEMY the calculated quantity of pure phosphoric acid, but the experiment was unsuccessful. When a solution of hydro-disodic phosphate is heated, and freshly prepared tungstic oxide is added, in small portions at a time, the oxide is readily dissolved with formation of a colorless or faintly bluish liquid. The solution gave crystalline precipitates with baric chloride and argentic nitrate, but the salts formed proved on analysis to be only mix- tures. An ammonium salt was prepared by adding ammonic nitrate and nitric acid to the solution of the sodium salt. The ratio of tung- stic to phosphoric oxide in the white crystalline salt formed was as 20:1 very closely ; but this does not lead to any inference as to the formula of the sodium salt in solution. Tribasic sodic phosphate also dissolves tungstic oxide readily, and the same is true as regards am- monic phosphate ; but I could not obtain definite salts from either solution. Potassic phosphate dissolves tungstic oxide very slowly, and only by long boiling. No definite compound was formed in this case. When hydro-disodic phosphate and tungstic oxide are fused together the latter dissolves and forms a colorless fused mass. This is soluble in water, but, as in the other cases, gives no single well defined salt. I have made no experiment to determine whether phospho-tung- Btates of the lower orders dissolve freshly precipitated tungstic oxide so as to form the higher terms in the series. The extraordinary amount of time and labor which I have already spent upon the subject must be my excuse for leaving this and many other interesting points to other investigators. There is no part of the subject which will not amply repay a new and careful study. ARSENIO-TUNGSTATES. When solutions of alkaline tungstates and arsenates are mixed it frequently happens that white crystalline precipitates are formed, the supernatant liquid becoming strongly alkaline. These precipitates are arsenio-tungstates, and, as might be expected, correspond in a general way to the class of phospho-tungstates already described. They appear to be as a rule less well defined than these last, and, so far as I have been able to discover, exhibit no character of special interest. In analyzing the few salts of this series which I have studied, I have em- ployed the same methods which I have used for the analysis of the ph(i.-pho-tungstates. Only the conditions are necessarily in some re- spects different. Arsenic and tungstic oxides were precipitated together OP ARTS AND SCIENCES. 135 by mercurous nitrate, mercuric oxide being employed to secure per- fect neutrality. The mercurous salt was then separated upon an asbestos filter, and, after drying, ignited — finally with the blast-lamp — until a constant weight was obtained. In this manner very nearly the whole of the arsenic oxide was volatilized. There is no danger of a reduction to metallic arsenic if the crucible containing the asbestos and precipitate is placed within another, covered, and then cautiously heated. The arsenic oxide is best determined as ammonio-magnesian arsenate, using a large excess of magnesia-mixture in the first precipitation. Two precipitations are necessary to secure a perfect separation ; the salt is to be collected on an asbestos filter, and dried in the usual man- ner. In determining water, or water and ammonia, in these salts, it is best to ignite with a weighed quantity of fused sodic tungstate, as sug- gested to me by Dr. Gooch ; only it must be observed that the fused tungstate is rather deliquescent. With all these precautions fairly good results may be obtained. I endeavored to separate arsenic from tungstic oxide by boiling the salt with dilute phosphoric acid, reducing the arsenic to arsenous acid by sulphurous acid, and then precipi- tating by sulphydric acid as As2S8. This method appears to give a complete separation, but is very tedious and circumstantial. Acid 3-atom Potassic Arsenio-tungstate. — When 12:5 acid potassic tungstate is dissolved, and a solution of potassic arsenate, As04KII2, is added, a white very fine-grained precipitate is formed. When an excess of the arsenate is employed, and the mixed solutions are evap- orated upon a water-bath, a perfectly white insoluble salt is separated, which is the acid arsenio-tungstate 6 W03 . As,05 . 3 K,0 . 3 H20. The formation of this salt may be represented by the equation 12 W03 . 5 K20 + As20. . K20 . 2 H20 -f 4 H20 = 2 {6 W03 . As20. . 3 K20 . 3 H20} . For analysis the salt was washed upon a filter with hot water, then dried upon paper, and afterward — as the mass remained pasty — upon a water-bath, where it finally dried to a hard white mass. Of this salt, — 0.8276 gr. gave 0.5902 gr. W03 = 71.31% 0.7197 gr. " 0.5130 gr. " =71.28% 1.9815 gr. " 0.3841 gr. As20KMg2(MII4)2 + H20== 11.73% As206 1.3507 gr. lost on ignition 0.0357 gr. water = 2.04% 136 PROCEEDINGS OF THE AMERICAN ACADEMY The formula requires : — 6 WO, 1392 Calc'd. 71.05 71.31 71.28 As205 3 K20 3H20 230 283 54 11.75 14.45 2.75 11.73 14.33 (difE.) 2.64 1959 100.00 The salt dissolves readily in alkaline hydrates. Its chief interest lies in the fact that it serves to establish the existence of a 6-atom series of arsenio-tungstates. Acid 6 : 4 Ammonium Salt. — When amnionic arsenate As04NII4 and neutral sodic tungstate are dissolved together, no precipitate is formed at first, but after a short time a dense white crystalline salt is thrown down, which after twelve hours becomes abundant. Boiling water dissolves this salt readily, but it does not crystallize well from the solution, forming only a thick white mass. If this mass be dissolved in water, nitric acid added in excess gives a white crystalline precipitate, but slightly soluble in the acid liquid and in water. Of this salt, after washing with cold water, — 0.8255 gr. gave 0.6013 gr. W03 = 72.84% 1 .9486 gr. " 0.3980 gr. As.,OsMg2(NH4)2 -f H20 = 12.36 % As 20. 1.2494 gr. « 0.2635 gr. NH4C1 =10.25% The analyses agree — though not very closely — with the formula 6 W03 . As205 . 4 (NH4)20 . 2 H20 + 3 aq, which requires : — 6 W03 1392 Calc'd. 72.50 72.84 As205 230 11.98 12.36 4 (NH4)20 208 10.83 10.25 5 H,0 90 4.69 4.55 (diff.) 1920 100.00 The differences are, I think, not greater than may be expected in cases in which the salt analyzed cannot be purified by recrystalliza- tion. Normal 16 : 6 Silver Salt. — I obtained this salt by the following process : 100 gr. neutral sodic tungstate and 25 gr. arsenic acid were dissolved together and the solution boiled for some time, then filtered and evaporated upon a water-bath. After a day much sodic arsenate separated in crystals. The filtrate from these crystals deposited a OP ARTS AND SCIENCES. 137 white' indistinctly crystalline mass. This was redissolved and potassic bromide added in excess, when an abundant white crystalline fine-grained precipitate was thrown down, which was drained on the filter-pump, and then washed with cold water. This was dissolved in much boil- ing water, and argentic nitrate added, when a white crystalline salt was thrown down mixed with brownish-red crystals of argentic arsenate. The mass was treated with very dilute nitric acid, which readily dis- solved the arsenate, the undissolved portion appearing under a lens as made up of opaque white acicular crystals. These were well drained, washed with cold water, and dried on paper by pressure, when the mass showed a faint yellowish tint. The salt is but slightly soluble in cold water. Of this salt, — 0.7488 gr. gave 0.5024 gr. W03 = 67.09% 0.7531 gr. " 0.5067 gr. " = 67.29% 2.0321 gr. " 0.6147 gr. AgCl = 24.45% Ag20 1.0215 gr. « 0.3096 gr. " = 24.48% " 0.9209 gr. lost on ignition 0.0340 gr. water = 3.69% The analyses correspond tolerably well to the formula 16 W03 . As2Os . 6 Ag,0 -4- 11 aq, which requires : — Calc'd. 16 W03 3712 67.10 67.09 67.29 As265 230 4.16 4.65 (diff.) 6 Ag20 1392 25.16 24.45 24.48 11 H20 198 3.58 3.69 5532 100.00 I do not place implicit confidence in the formula given, as the two determinations of argentic oxide are too low. It is very possible that the salt was slightly decomposed by the dilute nitric acid employed to remove the arsenate. But in any case it is proved that arsenio-tung- states exist in which the ratio of W08 to As205 is higher than 6:1, and a method of obtaining such compounds is pointed out. General Conclusions. — The general results of my investigation of the phospho-tungstates may be stated briefly as follows : — 1. The phospho-tungstates form a series of which the lowest term probably contains six atoms of tungstic to one of phosphoric oxide, and the highest, twenty-four atoms of tungstic to one of phosphoric oxide. 2. At least the greater number of phospho-tungstates contain an even number of atoms of tungstic oxide. The homologizing term for these cases is therefore 2 WO,, 138 PROCEEDINGS OP THE AMERICAN ACADEMY 3. The highest number of atoms of base observed in any case is six (old style), which implies that each acid contains twelve atoms of hydroxyl. 4. In all cases observed the number of atoms of hydroxyl replaced by a monatomic metal is even. 5. One instance occurs in which two acid phospho-tungstates of different orders appear to unite to form a definite compound ; but this case admits of a different explanation. 6. In all phospho-tungstates studied the number of atoms of base or of hydroxyl is more than sufficient to saturate the phosphoric oxide present, if we admit that the acid is 1 2-basic. At least a part of the hydroxyl or base must therefore be united to tungstic oxide. For greater facility of comparison I have brought together the formulas of all the compounds described in this paper, writing them both with the old and the new notation. 24 W03 . P206 . 6 H20 + 47 aq W24P2071 ( HO )12 + 47 aq 24 W03 . P205 . 6 H20 + 34 aq W24P2On(HO)12 + 34 aq 24 W08 . P206 . 6 H20 + 55 aq W24P207l(HO)12 + 55 aq 24 W08 . P205 . 2 Na20 . 4 H20 +23 aq W24P2071(NaO)4(HO)8 + 23 aq 24 W08 . P206 . 3 K20 . 3 H20 + 8 aq W24P207l(KO)6(HO)6 + 8 aq 24 W03 . P206 . 3 K20 . 3 H20 + 14 aq W24P2071(KO)6(HO)6 + 14 aq 24 W08 . P205 . 3(NH4)20.3H20 + 26aq W24P.207l(NH40)6(HO)6 + 2G aq 24 W03 . P205 . 3 BaO . 3 H20 + 43 aq W24P.2071(Ba02)3(HO)6 + 43 aq 22 W03 . P205 . 2 K20 . 4 H20 + 2 aq W22P2065(KO)4(HO)8 + 2 aq 22 W03.P205.3(NH4)20.3H20 + 18aq W22P2065(NH40)6(HO)6 + 18 aq 22 W03 . P205 . 2 Na20 . 4 H20 + 5 aq W22P2065(NaO)4(HO)8 + 5 aq 22 W08 . P205 • 4 BaO . 2 H20 + 39 aq W22P2065(Ba02)4(HO)4 + 39 aq 20 W03 . P203 . 6 BaO + 48 aq W20P2O69(BaO2)6 + 48 aq 18 W03 . P206 . 6 K20 + 23 aq W16P2053(KO)12 + 23 aq 18 W03 . P205 . 6 K.,0 + 30 aq W18P2053(KO)12 + 30 aq 18 W08 . P205 . K20 . 5 H20 + 14 aq W18P2053(KO)2( HO)10 + 14 aq 16 W03 . P205 . CaO . 5 H20 + 3 aq W16P2O47(CaO2)(HO)10 + 3 aq 16 W03 . P205 . 4 K20 . 2 H20 + 19 aq Wi6P2047(KO)8(HO)4 + 19 aq 16 W08 . P205 . 6 (NH4),0 + 10 aq W16P2047(NH40)12 + 10 aq 14 W03 . 2 P206 . 5 Na20 + 42 aq 6 W03 . As2Os .31,0.3 H20 W6As2027(KO)6(HO)6 6 W03.As206.4(NH4)20.2H20 + 3aq W6As2027(NH40)8(HO)4 + 3 aq I 1G W03 . As205 . 6 Ag20 + 11 aq W16As2047(AgO)12 + 11 aq OP ARTS AND SCIENCES. 139 In writing these formulas I have assumed that all the acids are 12-basic, since it has been shown that there are salts of the sixteen-, eighteen-, and twenty-atom series which correspond with this view. I shall resume the discussion of the subject in connection with the phospho-molybdates, and at the same time examine in detail the ques- tion of the existence of a distinct class of pyro-salts of the tungstic and inolybdic series. {To be continued.) r s-r *"> iMti ',-,. 1.9024 gr. " 0.6029 gr. " =4.01% " 1.2334 gr. « 0.6262 gr. NH4C1 = 4.23% (NH4)20. The salt was dried for some time in pleno over sulphuric acid, and had evidently lost water of crystallization. If we deduct the remain- ing water, 0.94%, and calculate the analysis for an anhydrous salt, we have for the formula 22 MoOs . P205 . 3 (NH4)20 ; Calc'd. 22 Mo08 3168 91.41 91.68 PA 142 4.09 4.05 3 (NH4)20 156 4.50 4.27 3466 100.00 72 PROCEEDINGS OF THE AMERICAN ACADEMY In another preparation, — 1.0324 gr. lost on ignition with W04Na2 0.0922 gr. — 8.93% "NH3 and H20 2.0670 gr. gave 0.1255 gr. P20TMg8 = 3-88% P2°s 2.0352 gr. « 0.1220 gr. " " = 3.84% " These analyses lead to the formula 22 MoOs . P20,5 . 3 (NH4)20 -f- 9 aq, which requires : — CalcM. 22 MoOg 3168 87.32 PA 142 3.91 3 (NH4)20 156 4.29 9H20 162 4.48 3628 100.00 17.21 3.84 8.77 8.93 If from the analyses of the two salts above described we calculate the composition of the combination of molybdic and phosphoric oxides supposed to be isolated, and compare this with the percentages calcu- lated upon the two hypotheses of a ratio of 22 : 1 and a ratio of 24 : 1, re have : — Calc'd. I. 11. Calc'd. 22 MoO. 3168 95.76 95.76 95.76 96.06 3456 24 MoO< r.o. 142 4.24 4.24 4.24 3.94 142 PaO,' 3310 100.00 100.00 100.00 100.00 3598 In both cases the phosphoric oxide was precipitated twice, but the ammonia-magnesian phosphate was not treated with amnionic sulphide. According to the results of Dr. Gooch already cited, the probable error of this method does not exceed 1 % in excess of the quantity of phosphoric oxide present. It appears, therefore, that the correction to be applied to the phosphoric oxide in the above analyses does not, at most, exceed 0.04%. The mean of Dr. Gooch's analyses would require a deduction of 0.02% only. The yellow ammonium' salt analyzed by Eammelsberg corresponds to the formula 22 MoO„ . P2Os . 3 (NH4)20 -f 12 aq, which requires (Rammelsberg) Calc'd. 22 MoO, 3168 86.04 86.45 PA 142 3.86 3.90 3 (NH4)20 156 4.24 3.25 12 11,0 216 5.86 5.77 3682 100.00 99.37" OF ARTS AND SCIENCES. 73 Rammelsberg gives these figures as the means of several analyses which agree well with each other, but it must be admitted that a closer correspondence with the percentages required by the formulas would have been desirable. The comparison is not given in his paper. The air-dried salt loses all its water over sulphuric acid. The three atoms of basic water, if we assume their existence, must there- fore be united by a very feeble affinity. Rammelsberg has also analyzed the corresponding potassic salt of the same series. I here give his results, for the sake of comparison with the formula : — 22 Mo03 3168 Calc'd. 83.17 84.43 PA 142 3.73 3.78 3 K20 283 7.43 6.86 12 H20 216 5.67 5.55 3809 100.00 100.62 This salt loses all its water between 120° and 140°. In judging the results of these analyses, as well as of those which I have given, it must be carefully borne in mind that the salts themselves cannot be recrystallized, and that consequently their absolute purity cannot be guaranteed. Moreover, if — as I believe I have shown — there are very similar salts which represent three series in which the ratios of the molybdic and phosphoric oxides are respectively as 24 : 1, 22 : 1, and 20: 1, we may, at least occasionally, have mixtures of the salts of three, or of any two series. The difficulty here is precisely that which occurs in the case of the phospho-tungstates. 44 : 2 Acid Potassium Salt. — This salt was prepared by boiling a mixture of potassic molybdate and phosphate with nitric acid in excess, when a beautiful yellow crystalline powder separated. Thia was washed with cold water and dried on woollen paper. Of this salt, — 0.9850 gr. lost on ignition 0.0521 gr. = 5.28% water. 0.8983 gr. gave 0.7943 gr. Mo03 -4- P205 = 88.42% 2.0617 gr. gave 0.1201 gr. P207Mg2 = 3,72% These analyses lead to the formula 44 Mo03 . 2 P20. . 5 K20 . H20 + 21 aq, or 22 MoO, . P205 . 3 K20 -f 22 MoO, . P20, . 2 K.0 . H,0 -f 21 aq, which requires : — 74 PROCEEDINGS OP THE AMERICAN ACADEMY Calc'd. 44 Mo03 6336 84.62 84.70 2 P205 284 3.79 3.72 5 K20 472 6.30 6.30 (diff.) 22H20 396 5.29 5.28 7488 100.00 The salt is therefore the acid salt corresponding to a neutral salt with the formula 22 Mo03 . P20. . 3 K20. Rammelsberg's analyses agree better with the formula of the acid salt given above than with that of the neutral compound assumed by him. Twenty Atom Series. — The only salt of this series which I have obtained is one of ammonium prepared like the salts already described, having like these a fine yellow color and a very fine-grained crystalline structure, and like them but slightly soluble in water. Of this salt, — 1.0936 gr. lost on ignition with W04Na2 0.0729 gr. = 6.66% NH3 and H20 1.8183 gr. lost on ignition with W04Na2 0.1155 gr. = 6.35% NH3 and H20 0.8862 gr. gave 0.6153 gr. NH4C1 = 4.12% (NH4)20 1.3213 gr. gave 0.6224 gr. P2OrMg2 = 4.19% P.205 1.5135 gr. gave 0.6349 gr. P207Mg.2 = 4.31% P205 The salt was dried on a water-bath, and afterward over sulphuric acid. The phosphoric oxide was precipitated twice, but not treated with ammonic sulphide. The analyses lead to the formula 60 MoO„ . 3 P20. . 8 (NH4)20 . H20 -f- 11 aq. which requires : — 60 MoOs 8640 Calc'd. 89-09l 93.48 4.39) 89-21 1 93.52 4.31 4.19 ) 3 P20. 426 8*(NH4)20 416 12 H20 216 4'29i 6.52 2.23) tl! I6-50 2.54) 9698 100.00 If we calculate the composition of the mixed oxides of molybdenum and phosphorus existing in this salt we have : — OF ARTS AND SCIENCES. <£> CalcM. 20 Mo03 2880 95.30 95.39 P203 142 4.70 4.61 3022 100.00 100.00 It will be seen that the ratio is here very nearly as 20 : 1. This may however be merely accidental, and farther researches are necessary to fully establish the existence of a 20-atom series. According to Debray a solution of argentic nitrate gives with one of phospho-molybdic acid a precipitate which soon becomes crystalline, and which has the formula 20 M0O3 • P2°5 • 7 Ag-2° + 24 aq- Such a salt would possess a twofold interest, first, as another evi- dence of the existence of a 20-atom series of phospho-molybdates, and, secondly, as showing that the acid of the series may unite with more than six atoms of base. On mixing the two solutions as above, I ob- tained a precipitate in small indistinct crystals of a greenish yellow color. These crystals were soluble in hot water, but the solution was quickly decomposed with precipitation of a white powder. Under the micro- scope with a high power and transmitted light the salt appeared to consist of small tabular crystals mixed with a few long yellow prisms of very different habitus. Of this compound, — 1.3G04 gr. lost by ignition with W04Na2 0.0692 gr. water = 5.08% 2.109!) gr. gave 0.8287 gr. AgCl = 31.03% Ag20 0.G733 gr. gave 0.2619 gr. AgCl = 31.44% Ag20 2.1099 gr. gave 0.0928 gr. P,OrMg2 = 2.81 % P,0, The phosphoric oxide was determined in the filtrate from the ar- gentic chloride by double precipitation and treatment with amnionic sulphide. The ratio of the molybdic to the phosphoric oxide is as 21 : 1, but the formula which most nearly represents the analysis is 22 Mo03 P205.7Ag2< > + 14 aq, Inch requires, — Calc'd. 22 M0O3 3168 61.08 60.57 PA 142 2.74 2.81 7Ag20 1624 31.32 31.44 31.63 14 H.,0 252 5186 4.86 100.00 5.08 76 PROCEEDINGS OF THE AMERICAN ACADEMY The only conclusion which can fairly be drawn from the analysis is that there is at least one phospho-molybdate in which the number of atoms of base exceeds three. It is certain that the salt does not rep- resent a perfectly definite and homogeneous compound, and it may possibly be a mixture of the 20-atom salt, 20 Mo03 . P20, . 6 Ag20, and an acid molybdate of silver, 2 Mo03 . Ag20, nearly in atomic pro- portions. By dissolving the salt in nitric acid and evaporating, Debray obtained another salt in small brilliant yellow crystals. For this salt he proposes the formula 20 MoOa . P,05 . 2 Ag20 + 7 aq, but as usual he has given no analyses. Eighteen Atom Series. — I have myself met with no salts belonging to this series, but according to Finkener* there are sodium salts corre- sponding to the general formula 18 Mo03 • P2°s (3 — a) Na20 + (25 + x) aq. These salts are yellow and easily soluble. Sixteen Atom Series. — 16:3 Ammonium Salt. — In preparing the 5 : 3 atom ammonium salt a white crystalline precipitate was formed, insoluble in cold, but soluble with decomposition in much boiling water, and easily soluble in ammonia. In this salt dried over sulphuric acid, — 0.5100 gr. lost by ignition with W04Na2 0.0722 gr. = 14.16% NH3 and H20 1.1653 gr. gave 0.1259 gr. NH4C1 = 5.25% (NH4)20 0.8114 gr. gave 0.0658 gr. P207Mg2 = 5.19% P205 The analysis corresponds with the formula 16 Mo03 . P205 . 3 (NH4)20 + 14 aq, which requires, — Calc'd. Found. 16 M0O3 2304 80.73 80.65 P205 142 4.97 5.19 3 (NH4)20 156 5.46 5.25 14H20 ' 252 8.84 8.91 2854 100.00 Loc. cit., p. 1639. OP ARTS AND SCIENCES. 77 Five to One Series. — Salts of this series were discovered at an early period in the history of the subject by Zenker* The ammonium salt was analyzed by Zenker! and Wernicke,! and recently by Ram- melsberg.§ Debray obtained the same salt, but has published no analyses. Rammelsberg also obtained the corresponding potassium salt, as well as an acid salt of the same series. The alkaline salts are colorless, and separate in well-defined crystals, which are usually easily soluble in water. The acid of the series, as Debray has stated, can- not be obtained by the decomposition of its salts, being resolved by acids into free phosphoric acid and salts of the 24-atom series. The decomposition may probably be expressed by the equation 24 (5 Mo03 . P20,5 . 3 H20) = 5 (24 Mob, . P2(X . 3 H,0) + 19 (P205 . 3 H20). All the neutral salts are tribasic (old style) or more correctly hexa- tomic, but well-defined acid salts exist in which the ratio of the molyb- dic oxide to the lixed base is as 10: 5. Such salts have been obtained by Rammelsberg and by myself. The salts of the higher series are de- composed by alkalies, as stated by Debray, salts of the 5-atom series and alkaline molybdates being formed. Conversely, when a mineral acid is added to a solution of an alkaline salt of the 5-atom series, a salt of a higher series is formed, frequently as a yellow crystalline precipitate. The neutral salts of this series hitherto described have respectively the formulas 5 MoO, . P.,0., . 3 K.,0 -f 7 aq. 5 MoO,' . P2Os . 3 (NH4),0 -4- 7 aq. 5 M0O3 . P2Os . 3 Na20 + 14 aq. 5 M0O3 . P,05 . 3 Ag20 -f 7 aq. 5 : 3 Phospho-molybdate of Ammonium. — This beautiful salt ap- pears, as already stated, to have been first obtained by Zenker. It is readily obtained by dissolving together five molecules of amnionic molybdate and two of amnionic phosphate, and evaporating the solu- lution. when beautiful prismatic crystals, with a glassy lustre, separate. These may easily be purified by recrystallization. The salt is readily soluble in hot, less easily in cold water. The solution has an acid reaction. Zenker's analyses, as well as those of Werncke, agree closely with the formula 5 MoO., . P205 . 3 (NH4)20 -f 7 aq, * Journal fur prakt. Cheinie, Iviii. 256. t Lon. cit. \ Zeitschrlft fiir Analyt. Chemie, .\iv. 12. § Loc. cit. 78 PROCEEDINGS OP THE AMERICAN ACADEMY in which formula the phospho-molybdic acid is regarded as tribasic. Debray gives the same formula, without details of analysis, and Rammelsberg has very recently again analyzed the salt, confirming the results of Zenker. Tbe salt in question is particularly interest- ing, first, because the number of atoms of molybdic oxide is uneven ; and secondly, because the basicity of the acid appears to be 3, and not 6, even when the salt has separated from neutral solutions. Jorgensen * has described two well-defined crystalline salts belonging to this series and having according to his notation respectively the formulas Co2 (NH3)10C12. (5 Mo03 . 2 P04H) and Cos(NH8)10Cla . (5 MoOs . 2 P04NH4). I should write these 5 Mo08 . P2Os . Co2(NH3)10Cl2O2 . H20 and 5 Mo03 . P205 . Co2(NH3)10Cl2O2(NH4)2O. It will readily be seen that both salts correspond to the acid repre- sented by the formula 5 Mo03 . P205 . 3 H20. Acid 10 : 5 Ammonium Salt. — When ammonic phosphate is dis- solved in boiling water, and molybdic oxide is added in small portions at a time, the oxide readily dissolves, but a greater or less quantity of a white insoluble crystalline salt is formed. The filtrate deposits on evaporation large colorless crystals, which appear to be either trimetric or monoclinic. Of these crystals, — 1.1126 gr. lost on ignition with W04Na2 0.2076 gr. = 18.66% NH3 and H20. 1.2962 gr. " " " 0.2425 gr. = 18.71% " 1.21 G5 gr. " " " 0.2247 gr. = 18.47% " 0.9263 gr. gave 0.1912 gr. P207Mg2 = 13.20% P205 1.0540 gr. " 0.2196 gr. " =13.32% " 1.1824 gr. " 0.3018 gr. NH4C1 = 12.41% (NH4)20 1.0183 gr. " 0.2563 gr. « =12.23% 1.6430 gr. " 0.4168 gr. " = 12.32% " * Journal fiir prakt. Chemie, [2.] xviii. 209. OF ARTS AND SCIENCES. 79 The analyses lead to the formula 10 MoO, . 2 P205 . 5 (NH4)20 . H20 -f G aq, or 5 MoOs . P,0., • 3 (NH4)20 + 5 Mo03 . P 20. . 2 (NH4)20 . H20 + G aq, which requires : — Calc'd. Mean. 10 Mo03 1440 68.24 68.13 2 P205 284 13.46 13.26 13.20 13.32 5 (NH4)20 260 12.32 12.32 12.41 12.23 12.32 7 H20 " 126 .5.98 6.29 6.15 6.34 6.39 2110 100.00 The phosphoric oxide was determined by double precipitation only, without subsequent treatment with ammonic sulphide. The percent- age is a little lower than that required by the formula, which is unusual ; but the general agreement of the analyses with the formula is satisfactory. Rammelsberg has described an acid potassium salt with the formula 10 MoO, . PL)0,, • 5 K20 . H20 -f 19 aq. It is therefore at least probable that we shall find another ammonia salt with 20 atoms of water, and another potassium salt with 7 atoms. Zenker has described another potassic salt to which he gives the formula, — as I should write it, — 9 M0O3 . P205 • 4 KP • 2 H20 + 18 aq ; but the results of his analyses differ very widely from the percentages required by the formula, and on repeating his process I obtained only the 10:5 atom salt of Rammelsberg. The formula given above for this salt requires 11.11 % P205- I founu H.22%. Rammelsberg * has also described a white insoluble potassium salt to which he gives the formula 15 MoO, . P205 ■ ^ K20, but without any statement of his analyses. ARSENIO-MOLYBDATES. Compounds of arsenic and molybdic oxides have been described by Seyberth f and by Debray.J Sey berth obtained an acid with the formula, — as I should write it, — * Loc. cit. t Berichte der Cliem. Gesellschaft, 1874, p. 391. % Comptes Rendus, lxxviii. 1408. 80 PROCEEDINGS OP THE AMERICAN ACADEMY 7 MoOs As205 . 3 H20 + 11 aq, and the three corresponding salts : — 7 Mo03 . As2Os . (NTI4)20 . 2 H20 -f 4 H20 7 Mo03 . As205 . 3 BaO 7 Mo03 . As~05 . 3 Ag20. Debray obtained the acids and one or two salts of two different series, which may be represented respectively by the formulas : — 20 Mo03 . As205 . 3 H.vO + 24 aq 20 Mo08 . As205 . 3 K.'o 20 Mo03 . AsL"03 . 3 (NH4)20 6 Mo03 . As",05 . 3 H.,0 + 13 aq 6 M0O3 . As205 . 4 (NH4)90 + aq 6 Mo03 . As20.5 . (NHJ20 + 4 aq 6 Mo03 . As205 . Na20 + 12 aq. Debray considers the formula of the 20-atom ammonium salt as probable only, and regards the water determination in the corre- sponding acid as not quite certain. Neither Seyberth nor Debray has described the analytical methods employed, or given the details of the analyses. I have found it most advantageous to separate arsenic from mo- lybdic oxide by precipitating with magnesia mixture, redissolving the ammonio-magnesic arsenate, and precipitating a second time with ammonia after adding a little magnesia mixture. The ammonio-mag- nesic arsenate may be digested with ammonic sulphide without de- composition ; but after the second precipitation it does not retain molybdic oxide, and the subsequent treatment is therefore unneces- sary. To determine the sum of the molybdic and arsenic oxides I precipitate the two together with mercurous nitrate and mercuric oxide, in the manner already described for the estimation of molybdic and phosphoric oxides, filter upon paper, and after drying roll up the filter and its contents and ignite cautiously in a porcelain crucible. By slow and careful heating the filter may be completely burned with- out loss of molybdic or arsenic oxides, this result being attained by the oxygen of the mercurous and mercuric oxides present. A weighed quantity of sodic tungstate is then to be added in fine powder, the mass well mixed in the crucible, and then cautiously heated until mercury is completely expelled, and after cooling a white fused mass remains. A second or even a third heating is necessary to insure a OP ARTS AND SCIENCES. 81 perfectly constant weight. The difference between the percentage of arsenic oxide, As.,0., and the sum of the percentages of the arsenic and molybdic oxides, gives the percentage of molybdic oxide with a very fair degree of approximation. In these salts the water must always be determined by ignition with sodic tungstate or some similar compound, since both arsenic and molybdic oxides are volatile. Sixteen to one Series. — When solutions of ammonic arsenate and acid molybdate (7 : 8 salt) are mixed, a beautiful white crystalline pre- cipitate is thrown down, which is very insoluble in cold water but dissolves slightly in boiling water, giving, however, a turbid solution. The salt is readily soluble in ammonia water. The portion analyzed was well washed on a filter with cold water aud dried on woollen paper. In this salt, — 1.1322 gr. lost on ignition with WO.Xa. 0.1C36 gr. NH3 and H20 = 14.45% 1.3389 gr. gave 0.2481 gr. XH4C1 = 9.00% (NHJ20 1.4276 gr. " 0.1478 gr. AsX>-Alg2 = 7.68% As205 The analyses lead to the formula 16 MoO, . As,05 . 5 (NII4),0 . H20 -f 8 aq. wdiich requires : — Calc'd. I6M0O3 2304 77.94 1 77.97 ) As,05 230 7.78 J80"72 7.68 j 8°-65 5(NHJ20 260 8.79|142g 9.00 j ^ .00) .45} 9 H20 162 5.49 j 5, 2956 The salt may have lost a little ammonia in drying. When potassic arsenate and acid molybdate are mixed, a similar salt is formed. A solution of arsenic acid gives at once in solutions of acid ammonic or potassic molybdate a beautiful white crystalline precipitate, insoluble in cold water, but soluble in a large quantity of boiling water, forming cloudy solutions which pass freely through a filter. These may serve as -tarting-points for new investigations. The arsenio-molybdate above described is not perceptibly altered by long boiling with nitric acid, but the existence of higher compounds containing 22 or 24 molecules of molybdic to one of arsenic oxide appears at least extremely probable. The phospho-molybdates and arsenio-molybdates now known with some degree of certainty are as follows : — VOL. XVII. (n\ s. ix.) 6 82 PKOCEEDINGS OP THE AMERICAN ACADEMY 24 MoO, . P205 . 6 H20 + 47 aq Mo24P2071(HO)12 + 47 aq 24 MoO, • P205 . 6 H20 + 43 aq Mo24P2071( HO)12 + 43 aq 24 MoO, . P205 . 6 H20 + 24 aq Mo24P2On( HO)12 + 24 aq 24 Mo03 . P205 . 2 K20 . 4 H20 Mo24P207l(KO)4(HO)8 24 M0O3 . P205 . CcO . 5 H20 + 18 aq Mo24P2O71(CcO2)(HO)10 + 18 aq 48 M0O3 . 2 P205 . 5 (NH4),0 . H20 + 16 aq Mo48P4O148(NH4O)10(HO)24- 16 aq 22 M0O3 • pJ°5 • 3 (NH4)20 . 3 H20 + 9 aq Mo22P20G5(NH40)6(HO)6 + 9 aq 22 MoOs . P205 . 3 (NH4)20 . 3 H20 + 6 aq Mo22P2065(NH40)6(HO)6 + 6 aq 22 M0O3 . P205 . 3 (NH4)20 Mo22P2068(NH40)6 22 M0O3 . P205 . 3 K20 . 3 H20 + 9 aq Mo22P2O65(KO)0(HO)6 + 9 aq 22 M0O3 . P205 . 7 Ag20 + 14 aq Mo22P2064( AgO)14 + 14 aq 44 Mo03 . 2 P205 . 5 K20 . H20 + 21 aq Mo44P4O130(KO)10(HO)2 + 21 aq 60 M0O3 . 3 P205 . 8 (NH4)20 . H20 + 11 aq Mo60P6O186(NH4O)16(HO)2 + 11 aq 18 Mo03 . P205 . Na20 . 5 H20 + m aq Mo18P2O53(NaO)2(HO)10 + m aq 18 M0O3 . P.,05 . 2 Na20 . 4 H20 + n aq Mo]8P2053(NaO)4(HO)8 + n aq 16 M0O3 . P205 . 3 (NH4)20 . 3 H20 + 11 aq Mo16P2O47(NH4O)0(HO)6 -f 11 aq 5 M0O3 . P205 . 3 Na20 . 3 H20 + 11 aq Mo5P2014(NaO )6( HO )6 + 11 aq 5 M0O3 . P205 . 3 (NH4)20 . 3 H20 + 4 aq Mo5P,014(NH40)6(HO)6 + 4 aq 5 M0O3 . P.,05 . 3 K20 . 3 H20 + 4 aq Mo5P2014(KO)6(HO)6 -f 4 aq 5 M0O3 . P205 . 3 Ag20 . 3 H20 + 4 aq Mo5P2014(AgO)6(HO)6 + 4 aq 10 M0O3 . 2 P205 . 5 K20 . HoO + 19 aq Mo10P4O34(KO)10(HO)2 + 19 aq 10 Mo03 . 2 P205 . 5 (NH4)26 . H20 + 6 aq Mo10P4O34(NH4O)10(HO)2+ 6 aq 20 M0O3 . As205 . 6 H20 + 21 aq Mo20As2O59(HO)12 + 21 aq 20 M0O3 . As205 . 3 K20 Mo20As2O62(KO)6 20 Mo03 . As205 . 3 (NH4)20 Mo20As2O62(NH4O)6 16 Mo03 . As205 . 5 (NH4)20 . H20 + 8 aq Mo16As2O47(NH4O)10(HO)2 + 8 aq 7 M0O3 . As.205 . 6 H20 + 8 aq Mo7As2O20(HO)12 + 8 aq 7 Mo03 . As205 . (NH4)20 . 5 H20 Mo7As2O20(NH46)2(HO)10 7 M0O3 . As205 . 3 BaO Mo7As2023( Ba02)8 7 Mo03 . As205 . 3 Ag20 Mo7As2028(AgO)6 6 M0O3 . As205 . 6 H20 + 10 aq Mo6As2017(HO)12 + 10 aq 6 M0O3 . As205 . 4 (NH4)20 + aq Mo6As2Ol9(NH40)8 6 M0O3 . As205 . (NH4)20 . 2 H20 + 2 aq Mo6As2O20(NH4O)2(HO)4 + 2 aq 6 M0O3 . As205 . Na20 . 5 H20 + 7 aq Mo6As2O17(NaO)2(HO)10 + 7 aq For the convenience of comparison with the corresponding com- pounds of tungsten, I have in writing these formulas as far as possible assumed that all the phospho-molybdic and arsenio-molybdic acids con- tain 12 atoms of hyclroxyl, or, in the language appropriate to the old notation, are six-basic. With the material before us, we are now pre- pared to discuss the question of the basicity of the phospho-tungstates OF ARTS AND SCIENCES. 83 and phospho-molybdates as well as of the corresponding arsenic com- pounds. The general results to which the study of the phospho-molybdates and arsenio-molybdates has led arc as follows : — 1. The phospho-molybdates form a series of which the lowest term contains five atoms of molybdic to one of phosphoric oxide, and the highest twenty-four atoms of the former to one of the latter. 2. As in the case of the phospho-tungstates, the greater number of the molybdenum compounds contain an even number of atoms of tung- stic oxide. The homologizing term is therefore 2 Mo03 for these cases. 3. By far the greater number of phospho-molybdates contain three atoms of fixed base (old style), or, in more modern language, may be considered as derived from acids containing six atoms of hydroxyl. Anhydrous compounds of this type occur, and are not always simply residues obtained by heating salts which may he considered as acid, as containing, for example. 3 K,0 . 3 ILO. It seems therefore necessary to admit the existence of acids of the general type n Mo08 . P205 • 3 H A which may, however, stand in the relation of pyro-acids to other acids of the type n MoO„ . P20. . 6 H20 . 4. On the other hand, while no single phospho-molybdate containing more than three atoms of fixed base for one of phosphoric oxide has been obtained in a state of indubitable purity, it is probable that there is at least one salt with six or more atoms of fixed base. I refer to the silver salt which I have expressed by the formula 22 Mo03 . PA • 7 Ag20 + 14 aq. 5. Setting aside the evidence derived from the analogy of the phos- pho-molybdates and phospho-tungstates, there is at present no sufficient proof of the existence of a series of phospho-molybdates or arsenio- molybdates containing more than three atoms of fixed base. Such purely negative evidence must not be too highly regarded. 6. As in the case of the phospho-tungstates, there exists a class of phospho-molybdates in which the ratio of the number of atoms of base to that of the number of atoms of phosphoric oxide is as 5 : 2, the num- ber of atoms of molybdic oxide being even. Since the publication of my work on the phospho-tungstates and 84 PROCEEDINGS OF THE AMERICAN ACADEMY arsenio-tungstates a paper by Sprenger * on the phospho-tungstates has appeared. Sprenger has examined, with a single exception, only the compounds of the 24 : 1 series, and has added a number of new salts, which, so far as regards their constitution, fully confirm my own results. The compounds described, belonging to the 24-atom series, are the following : — 24 W03 . PA . 3 H20 -f 58 aq 24 W03 . PA . 3 BaO + 58 aq 24 W03 . P203 . 2 BaO . H.,0 + 58 aq 24 WO, . P205 . BaO . 2 H20 -f 58 aq 24 W03 . P205 • 8 Cu20 -f 58 aq 24 W03 . P~05 . 3 Ag20 -J- 58 aq 24 W03 . P206 . Ag/i . H20 + 58 aq. Sprenger's formula for the octahedral acid agrees with that which I had given if we consider the acid as tribasic. The other salts which he has described are new, and form a valuable addition to our knowl- edge of this class of compounds. It is well worthy of notice, that in all of his salts, the acid included, the number of atoms of water is the same. The acid with 58 atoms of water of crystallization forms, there- fore, a complete and stable molecular structure in which 2, 4, or 6 atoms of hydrogen are replaceable. I do not recall any other series in which this constancy of crystalline water occurs, at least to the same extent. Sprenger has also obtained a salt of the 22-atom series which is of much interest. This is the barium salt 22 W03 . P205 . 7 BaO + 591 aq, and its special interest depends upon the fact, first, that the ratio of the tungstic to the phosphoric oxide is as 22 : 1, and, secondly, that the salt contains seven atoms of fixed base, or, in other words, must be con- sidered as derived from an acid containing at least fourteen atoms of hydroxyl. Sprenger asserts that he has obtained the corresponding acid, and it is to be hoped that he will pursue the subject farther. This barium compound furnishes additional evidence of the independent existence of a series in which the ratio is 22 : 1, and in addition it renders more probable the formula which I have given for Debray's silver salt, 22 Mo03 . P205 . 7 Ag20 -f 14 aq. From these two tolerably well-established cases it would appear that * Journal fiir prakt. Cheruie, xxii. 418. OF ARTS AND SCIENCES. 85 we are not justified in holding that the phospho-tungstates, phospho- molybdates, and corresponding arsenic compounds, have :i basicity of which the higher limit is six. I may here mention that I shall here- after describe a vanadio-molybdate of ammonium the analyses of which agree well with the formula 18 MoOa . y.J), . 8 (NH4)20 + 15 aq. The risk of drawing hasty conclusions from purely negative evi- dence is particularly great in discussing the degree of basicity of this whole class of compounds, but I shall endeavor to show that it is possi- ble to devise structural formulas which will embrace and explain all degrees of basicity which appear to be possible under the general con- ditions of the problem. "We may, as in the case of the alkaline tungstates already discussed, assume that both tungsten and molybdenum are hexatomic, and. a- in that case, we may start from the commonly received formula for po- tassic dichromate, Cr02 - O - K O Cr02 - O - K which may be equally well applied to hexatomic tungsten, O II O = W - O - K 0 O = AY - O - K II 0 If we further suppose that the separate terms of the structural formulas are symmetrically arranged, and take a 6 : 1 phospho-tung- state 6 W08 . Pg06 . 6 H20 or 6 W02 . P206 . (HO)12 as an illustration, we may, with at least a certain degree of proba- bility, express the structure as follows: — 86 PROCEEDINGS OP THE AMERICAN ACADEMY HO-W02 = W02-OH i " i HO-W02 — W02-OH i I HO-W02 — W03 - OH i i 0 o 1 I 3 (HO) = PO-O-OP = (OH), This formula explains the basicity of the acid satisfactorily. It also shows that, as six atoms of hydroxyl are united with phosphorus, and six with tungstic oxide, there should be theoretically a limiting case corresponding to an acid containing six atoms of hydroxyl, and represented by the formula 6 W03 . P205 . 3 H20 or 6 W02 . 03 . P205 . (HO)6 and structurally by wo2 = wo, i \ 0/ i W02 -0- wo2 II II W02 -0- wo2 0 o 1 I 3 (HO) = PO - O - OP = (OH), According to this view six atoms of hydroxyl are always associated with phosphorus, or, as the case may be, with arsenic. I consider this view of the subject by far the more probable. At the same time, how- ever, it is also possible that we may have the structural formula, HO- - wo2 = wo2 - -OH HO -W02 — wo2- -OH HO- -W02 — wo2 - -OH 0 1 / OP 0 0 PO in which all the atoms of hydroxyl are associated directly with tung- sten, and in the present state of our knowledge we can only decide the OF ARTS AND SCIENCES. 87 question upon general grounds of probability, so that our conclusions are at best uncertain. Finally, both formulas being at least possible, it may be that there are two isomeric modifications of each series of acids represented respectively by the formulas above given. There is no present evidence of the existence of such isomeric modifications in the case of phospho-tuugstates, phospho-molybdates, or the correspond- ing arsenic series ; but Marignac has shown that there are two isomeric series of silico-tungstates, which he calls respectively silico-tungstates and tungsto-silicates, and it may be that the difference between these depends upon differences in the mode of combination, precisely similar to those which I have pointed out above. I shall return to this sub- ject in the general discussion of my results. With respect to the two linking terms, 0 0 i i 0 0 1 1 i /0N , (HO) e PO - 0 - OP = (OH), and OP — PO no assumption is made which is not in perfect accordance with com- monly accepted views of the subject. We may now consider the most general case, that, namely, in which there are twenty-four atoms of tungstic or molybdic, to one of phos- phoric or arsenic oxide. We have for an acid of this type 24 W03 . P205 . 6 H20 or 24 W02 . 018 . P205 . (HO)12 and in accordance with the principles above laid down the structural formula may be written : — PROCEEDINGS OF THE AMERICAN ACADEMY wo2 = wo2 0 o wo2 = wo2 1 I 0 o wo2 = wo2 1 I 0 o wo2 = wo2 1 I O 0 wo2 = wo2 o o wo2 = wo2 o o wo2 = wo2 o o wo2 = wo2 o o n o o HO-W02 - W02-OH HO-W02 — W02-OH HO-W02 — W02-OH I I 0 o 1 I 3(HO) = PO-0-OP=(OH)a OP ARTS AND SCIENCES. 89 The case of an acid containing for twenty-four atoms of tungstic oxide six atoms of hydroxyl may easily be deduced from the above, upon the principle explained in the first example cited. Without again writing the cumbrous formula, it may easily be seen that the cases of acids containing more than twelve atoms of hydroxyl, if such really exist, are embraced in the above-given structural formula, and that in such cases there will be two variations in the mode of combination of the hydroxyl, similar to the two which occur when there are six or twelve atoms of hydroxyl. The structural formula given would explain sim- ply and naturally the tribasic character of all known phospho-molyb- dates and phospho-tungstates containing twenty-four atoms of metallic oxide, since in these all the hydroxyl may be united with phosphorus exclusively, or with tungsten exclusively. It only remains to consider the case of the compounds having for one atom of phosphoric or arsenic oxide an uneven number of atoms of metallic oxide, as, for instance, the 5 : 1 and 7 : 1 series. In these cases also there exists, as has been shown, a second and derived series, of which the successive terms are to be regarded as formed from those of the first series by doubling the mo- lecular weight and dropping an atom of fixed base. Thus, we have 5 Mo03 • P2°6 • 3 H2° a™3 10 M°03 • 2 P205 . 5 K,0 . H20 -f 19 aq 7 M( »Oa . As205 . 3 H20 14 W03 . 2 P205 . 5 Na20 . H20 -f- 42 aq 22 Mo08 . P206 . 3 H20 44 MoOa . 2 P206 . 5 K20 . H20 -j- 21 aq 24 MoOs . P~03 . 3 H20 48 MoOs . 2 P205 . 5(NH,)20 . H20+1 G aq All these salts appear to have an acid reaction. They may all be regarded as acid six-basic salts, and it is easy to see that the two series may be reduced to one by doubling the formulas of all the terms on the left, so that we shall have a single series, of which the successive terms are 10 MoO,, . 2 P20, . 6 H20 12 Mo08 . 2 As205 . 6 H20 14 W03.2 P205.6 H20 48 M0O3 . 2 P205 . 6 H20 This view in no wise excludes acids or salts of a higher degree of basicity. It has the advantage of bringing all the compounds to- gether, and of being more completely in accordance with what we know of the constitution of salts belonging to simpler types. The structural formulas which I have given — provisionally, of course — 90 PROCEEDINGS OF THE AMERICAN ACADEMY may easily be modified to suit this view, and will all be symmetrical, and suggestive of various possible isomerisms. The study of other complex inorganic acids will, doubtless, throw further light upon the subject, and to it I shall continue to devote my leisure. It already begins to appear that inorganic compounds may possess an unex[)ected degree of complexity, and that very wide fields of research in inorganic chemistry are still open. (2b be continued.)