Ql "A .V 777'.! 77 VK 1 )/•!'/'N/fM/\'A 7

purified hy alcohol is bent and I he water should first be boiled, to expel
carbon dioxide, then cooled. Standardize the solution by titniting n.gfi.inMt
the standard aeid, using methyl re<l or phenolphf halein. {See below,]

The sample should be ground to pass a 100-mesh sieve and it must be
well mixed. Weigh 0.<5 gm of the .sample on counterpoised glasses and
brush into a 250-ce Krlenmeyer flask. Moisten with water and then
pipette 75 ee of the standard acid into the flank. After effcrvertcenee hnn
nearly eenwd connect tin* flank with a. reflux condenser by means of a
rubber stopper. Boil gently for 5 minutes to expel carbon dioxide and to
insure complete Bolutkm of all enHbormte, then eool. Kinsc down the con-
donHcr, the stopper and the upper part of the flank. Add a drop of methyl
red or of phenolphthnlein and titrate the excess of ueid by means of stunditrd
Hodium hydroxide. (If phcnolphthalcin is used as indicator, the bane must
have been ntandftrdixed by UHI* of the name indieaior. Also, in this ease
wat(»r thai IB used for rinsing must be free from carbon dioxide mid it must
not be blown in from the Witnh bottle.)

(•alculate the alkalinity of the limestone irt termH of per cent of cideium
carbonate.

PHOSPHATES

Gravimetric, as Magnesium Pyrophosphate.'---Any phonpltate
that IK directly noluhlc* in water <»un contuin only mHulH <^f t.h<*
alkali groupt a« all cither phoHphat<\s hav<^ u n»Iaf iv«*ly low cle^riH*
of solubility. Solutions of phosphut^H or of phosphoric arid may
ho pn»(»ipitatc»d as ditnagnositmi utnmonium phosphate by UK*
addition of mugnoHitun chloride? or sulphate, the solution being
made banie with ainnumium h

NaOH ; fl)

The precipitate always <:ontainH a variable amount of

of crystullizution and it in tJic*rc*forc» not w<*i|(hc*d directly.
tion converts it definitely into inngneHmm pyrophosphute:

Igni-

In practice, the* c*orie(»ntrntion of ammonium hydroxide and of
ammonium salts must be regulated within certain limits to pre-
vent the partial precipitation of certain other phosphates
which cannot be* changed to pyrophonphate by Ignition. For
example, ?/;0n0magncHium ammonium phosphate, formed to

i