Chemical Science. 191 



heated in a tube, no water is evolved. Dr. Apjohn proposes to 

 call the substance iodo-bicyanide of potassium and mercury*. 



18. COMPOSITION OP TARTARIC ACID. 



By differences between his own estimate and that of Prout, Berze- 

 lius has been induced to re-examine the composition and number 

 of tartaric acid. He finds, from many experiments, that the tartrate 

 of lead is composed of 



Tartaric acid .... 37.2569 

 Oxide of lead . . . .62.7431 



Its atomic weight, therefore, is 828.05; hydrogen being 12.5, and 



oxide of lead 1394.5. 



Tartaric acid is composed of 



Hydrogen 3.0045 



Carbon 36.8060 



Oxygen 60.1895 



100 



which agrees with 5 atoms oxygen, 4 carbon, and 4 hydrogen (on 

 the assumption that water contains 2 atoms of hydrogen). Calcu- 

 lated in this way, the atomic weight should be 830.709, instead of 

 828.05, as above. Prout made it 830.709 by his analysis. 



Berzelius then examined the equivalent number of lead and its 

 oxide very rigorously ; and for this purpose prepared an extremely 

 pure oxide of lead, and reduced it by hydrogen at a sufficiently high 

 temperature. From the mean of six experiments, the results were, 

 per cent. 



Lead 92.8277 



Oxygen 7.1723 



And the atomic weight of lead 1294.29, instead of 1394.5, as 

 above ; hydrogen being 12.5. 



All the six results were between 1293 and 1296. 4 But if the 

 atom of hydrogen weighs 12.5, the atomic weight of lead, to be a 

 multiple of that number, should be either 1287 . 5 or 1300 ; and if 

 one of these numbers is the true one, my results ought to oscillate 

 about it, instead of oscillating, as actually happened, between 1293 

 and 1296.' Other considerations, drawn from the analysis of the 

 tartrate of lead, are by M. Berzelius considered as opposed to the 

 theory of multiple numbers of hydrogen f. 



19. RACEMIC ACID OR PARA-TARTARIC ACID. 



The following account of this acid is abstracted from Berzelius. 

 A manufacturer of tartaric acid at Thann, on the Upper Rhine, first 

 observed that with the ordinary acid appeared crystals of another 



* Phil. Mag., N.S., is-, 401. f Annales de Chimie, xlvi. 



