248 Dr. Thomas Thomson on [Oct. 



be accounted for by admitting its existence in the chloride 

 of tin employed. 



It is obvious that the greater portion of the racemic acid 

 wanting to make up the quantity introduced existed in the 

 first washings, or rather, in the liquid which had been sepa- 

 rated by the filter from the original mixture of the salts. 



The racemic acid in the second water was not sufficient 

 to saturate the protoxide of tin. If we suppose it to contain 

 subsesqui-racemate of tin, like the chalky precipitate, then 

 the racemic acid in it will be 4*05 gr. and the water 1-741 

 grs. This, subtracted from the whole racemic acid which 

 must have been present in the washings leaves 33-3 grs. for 

 the quantity in the first liquid, united to 13*39 grs. of pro- 

 toxide of tin. Now, this is almost exactly in the proportion 

 of 2 J atoms racemic acid to 1 atom of protoxide of tin. 



In what way the common salt, racemic acid, and oxide 

 of tin are united in this curious salt is not very clear ; but 

 that they form together a compound salt, is obvious from 

 this, that you cannot procure a particle of common salt 

 from it by concentrating its aqueous solution. It always 

 crystallizes in long needles, bearing a stronger resemblance 

 to nitre than to any other saline substance. 



XVIII. RACEMATED SUB-OXIDE OF MERCURY. 



This salt is easily formed, by mixing together solutions 

 of nitrated sub-oxide of mercury and racemate of soda, in 

 atomic proportions. The racemated sub-oxide precipitates 

 in the state of a white powder, having a slight mercurial 

 taste. Its sp. gr. is 2*525. At the temperature of 195°, 

 100 parts of water dissolve 0*0296 parts of this salt. 



20 grs. of this salt being exposed to the temperature of 

 380°, became black, and lost 0*3 gr. of its weight. From 

 this we see that the salt is anhydrous. The heat being raised 

 to rather more than 400°, mercury sublimed in the metallic 

 state, and a black matter remained, weighing 2*2 grs. It 

 was still racemate of mercury, or, at least, contained oxide 

 of mercury united to an acid. The running mercury col- 

 lected, by simply covering the sak on the sand bath with 

 an inverted glass, was 10*35 grs. 



To determine the composition of this salt, 20 grs. of it 

 were digested in caustic-potash, and the black matter re- 



