APPENDIX TO CHAPTER L1V.---TREATS SHRINKAGE. 409 that were not carried off from the mould through proper channels of venting the sand, or oxides and slag in the metal giving off gases that, in an effort to escape from the metal, become imprisoned in a casting, as seen at S, sample No. 22, Fig. 83. This is caused by reason of the metal solidifying before the gases could rise upward to find relief through the cope or top part of the mould, and which, if not well vented, or of a porous and fairly dry character, will then often hold the gases from going further and form cavities in the cope side of castings, such as seen at T in sample No. 23 of the same figure. A description of some special tests on shrinkage, contraction, specific gravity, and fusion that the author made and presented in a paper to the Western. Found-rymen's Association at Cincinnati, 1X97, are given in the following. Prior to these tests we did not possess any information as to what percentage of shrinkage there existed in iron when cooling from a fluid to a solid state. Realizing the advisability of obtaining such information, the author devised the following method of testing the shrinkage of the different metals shown in Table 86, page 411, and illustrated by Figs. 84 and 85. FIG. 84.—SHRINKAGE PATTERN ANI> TEST CASTING.de on their Hat as on their cud.