162 Dr. Thomas Thomson [Sept. 



to dryness in a gentle heat, left 122 grs. of raceinate of 

 soda. Now, it has been shewn above, that 105 grs. of the 

 crystals contain 80*991 grs. of real racemic acid, which 

 require for saturation 39*268 grs. of soda, making together, 

 120*259 grs. Hence, the salt was composed of 



Anhydrous racemate of soda . 120*259 or 12-25 

 Water 1*741 „ 0*177 



0*177 rather exceeds the sixth part of an atom of water. 

 This small quantity m^st have been mechanically lodged in 

 the salt. Thus, it appears that racemate of soda is an anhy- 

 drous salt. 



Tartrate of Soda. 



This salt crystallizes in four-sided prisms, rather oblique, 

 and usually terminated by a bihedral summit. It is com- 

 monly obtained in long needles, consisting of four-sided 

 prisms, and having somewhat of a silky lustre. It is not 

 altered by being left exposed to the air. 



The taste of this salt is saline, and it leaves in the mouth 

 an impression similar to that of glauber salt. Its sp. gr. 

 at 60° is 1*980. 100 parts of water at 61° dissolve 56*37 of 

 this salt. It is most sensibly soluble in alcohol. 



When heated it fuses, but speedily loses its water and falls 

 to powder. It then becomes brown, and, at last, black ; 

 swells up and burns with flame, leaving carbonate of soda 

 in the state of a gray salt. 



93*75 grs. of crystals of tartaric acid were saturated with 

 carbonate of soda, and evaporated to dryness in a gentle 

 heat. The silky crystals obtained weighed 151 grs. Now, 

 93*75 tartaric acid crystals contain 8*25 real acid, which 

 require 40 of soda to neutralize them. Hence, the salt was 

 formed of 



Anhydrous salt .... 122*5 or 12*25 

 Water 28*5 „ 2*85 



151*0 

 28*5 is very nearly 2J atoms of water. It is obvious, there- 

 fore, that tartrate of soda contains 2J atoms water. 



The absence of water in the crystals of racemate of soda 

 constitutes a remarkable difference between it and tartrate 

 of soda. It is singular that it should be specifically lighter 

 than a salt which contains 2J atoms of water. 



