98 Dr, Thomas Thomson [Aug. 



acid given by the French is preferable ; because vinic is the 

 name applied frequently on the Continent to tartaric acid. 

 In 1829 it was subjected to an examination by Gay-Lussac 

 and by Walchner, and the result of their experiments leaves 

 no doubt that it possesses peculiar properties. In 1830 it 

 was analyzed by Berzelius, who found its constituents and 

 its atomic weight the same as those of tartaric acid. On 

 that account he has given it the name of paratartaric acid. 



It seems to be formed during the process for extracting 

 tartaric acid from cream of tartar. When the tartaric 

 acid is crystallized for the first time, we observe mixed 

 with its crystals, a number of small needles. These on 

 examination are found to be racemic acid. Under the 

 microscope they assume the form of long oblique four- 

 sided prisms, usually terminated by an oblique face. By a 

 second crystallization they may be obtained in large doubly 

 oblique prisms. The terminating face is inclined to the 

 sides of the prism, at an angle of 75°, the one side to the 

 other at an angle of 68°. The longitudinal edges of the 

 prism (at least two of them) are usually replaced by tan- 

 gent planes, converting it into a six or eight-sided prism. 

 Not unfrequently one of the terminal edges of the prism 

 is also replaced by a plane, thus rendering the summit 

 of the prism two faces applied to each other like the roof 

 of a house. 



Tartaric acid forms very large but rather irregular crystals. 

 They may be obtained an inch and a half in length and 

 about 0*7 inch thick. The primary form of this acid is a 

 doubly oblique prism, but the angles are different. The 

 terminating face is inclined to the sides of the prism, at an 

 angle of 97*10°, and the one side to the other at an angle 

 of 88-30°. 



The edge is usually replaced by a very broad plane, 

 which renders the terminal face of the crystal triangular, 

 and gives to its upper surface the aspect of that variety of 

 calcareous spar called tete de clou. 



The lustre of racemic acid is silky, that of tartaric acid 

 glossy. The specific gravity of racemic acid crystals is only 

 1-600, while that of tartaric acid is 2-083. 



Racemic acid when heated to 150° loses its crystalline 

 form, and gives out 5*59 per cent, of water. At the same 



