138 Dr. Thomson's Experiments to determine the [Aug. 



Oxide of zinc 5*25 



Oxalic acid 2*5 



7-75 



Consequently it was a compound of two atoms oxide of zinc and 

 one atom oxalic acid. It appears from this that when oxalate 

 of zinc is exposed to the temperature of 550°, it loses not merely 

 its water, but likewise one half of its acid. 



When we drop oxalic acid into a solution of common blue 

 vitriol only one-half of the oxide of copper is precipitated in 

 combination with oxalic acid ; the remaining half is kept in 

 solution, probably in consequence of the excess of acid present. 

 Ammonia dissolves both oxalate of copper and oxalate of zinc. 



VIII. Tartaric Acid. 



The crystals of this acid, like those of oxalic, constitute a 

 hydrate composed of one atom real acid + one atom water. The 

 equivalent number for them is 9*5 ; consequently they are com- 

 posed of 



Tartaric acid = 8-375 



Water = 1-125 



9-5 



To verify the accuracy of this statement, it seems only neces- 

 sary to give the following experiments : 



1. 9*5 grs. of crystals of tartaric acid were dissolved in water, 

 and saturated with ammonia. 6-25 grs. of calcareous spar 

 were dissolved in muriatic acid, the solution was evaporated to 

 dryness, and the muriate of lime redissolved in water. These 

 two liquids being mixed together were very slowly evaporated to 

 dryness. Crystals of tartrate of lime separated in abundance. 

 Distilled water was poured upon this salt, and left upon it for 24 

 hours. It was then tested with oxalate of ammonia, but found 

 to contain no lime. A portion of it being mixed with muriate of 

 lime, and evaporated to dryness, the saline residue dissolved 

 completely in distilled water, and, therefore, contained no tar- 

 trate of lime. Thus we see that 9-5 grs. of the crystals of 

 tartaric acid contain exactly the quantity of acid necessary to 

 saturate 3-5 grs. of lime. 



When the tartrate of lime is dried at the temperature of 100°, 

 it retains very little water; for its weight was only 12 - 3 grains. 

 It undergoes decomposition at a much lower temperature than 

 oxalate of lime ; for it was partially destroyed in a heat, which I 

 do not think exceeded 500°. Probably if I had dried it at the 

 temperature of 212°, it would have been perfectly freed from 

 water. 



2. 9*5 grains of the crystals of tartaric acid were dissolved in 



