440 COMPOUND SALTS 



1 atom tartrate of potash 14-25 



1 atom tartrate of soda 12-25 



8 atoms water 9*00 



35-5 



Here the water of crystallization is twice as 

 great as in the two salts uncombined : for the 

 two salts contain each 2 atoms of water.* 

 Tartar jg. Tartar emetic. This well known salt is 



emetic. 



formed by boiling together cream of tartar and 

 glass of antimony in fine powder. The filtered 

 solution, when sufficiently concentrated, depo- 

 sites white coloured crystals of tartar emetic ; 

 the crystals are usually tetrahedrons ; it is com- 

 monly opaque, and very irregular in its shape ; 

 it requires about 14^ times its weight of cold 

 water to dissolve it, but it is much more soluble 

 in hot water. No accurate analysis of this use- 

 ful salt having been hitherto made, I took the 

 following method of ascertaining its constituents: 



* I have analyzed crystals of this salt after standing for a fortnight on 

 blotting paper in my laboratory, and found them composed of 



1 atom tartrate of potash 14- -25 



1 atom tartrate of soda 12-25 



10 atoms water . . 11-25 



37-75 



But I ascribed tliis difference to the difficulty of getting rid of the hygro- 

 metrical moisture. The crystals containing 8 atoms water, were large and 

 firm, and consequently, much freer from adhering moisture than the 

 small crystals formed in my laboratory. 



