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



this I did not urge the experiment, though I have little doubt 

 that a temperature of 600° would have reduced the weight to 

 exactly 8 grs. I was afraid of charring the salt, and thus depriv- 

 ing myself of the power of ascertaining whether the acid conti- 

 nued possessed of all its original characters. This experiment, 

 which was several times repeated with exactly the same result, 

 seems to me to leave no doubt that the oxalate of lime obtained 

 from 9 grs. of crystallized oxalic acid and 6-25 grs. of calcareous 

 spar, weighs, when perfectly freed from moisture, exactly 8 grs. 

 Now 3*5 grs. of it are lime ; consequently, the other 4*6 grs. are 

 oxalic acid. 



We see from this experiment, that 9 grains of the crystallized 

 oxalic acid contain precisely 4*5 grs. of true acid ; and that the 

 equivalent number for oxalic acid is 45. Hydrate of oxalic acid 

 then, or the crystals, are composed of 



4*5 acid = 1 atom, 



4*5 water = 4 atoms. 



Or they consist of 1 atom acid united to 4 atoms water. 



We see further, that when oxalate of lime is dried at a tem- 

 perature not exceeding 100°, it retains two atoms water ; for it 

 weighed 103 grs. Now 



1 atom oxalate of lime = 8-00 



2 atoms water = 2*25 



10-25 



So that a combination of two atoms water and 1 atom anhydrous 

 oxalate of lime weighs 10-25, which differs only by 0*05 gr. or 

 rather less than half a per cent, from 103, the number actually 

 obtained. 



The knowledge of this fact suggests a mode of determining the 

 quantity of lime in mineral bodies, which 1 have been in the 

 habit of following for some time past. The method is this. 

 Throw down the lime by means of oxalate of ammonia, separate 

 the oxalate of lime upon a filter, wash it, and dry it in a temper- 

 ature not higher than 100. Ascertain its weight, and multiply 



o. t 



it by .[ ■ ' or by 0-341 ; the product is the quantity of lime con- 

 tained in the oxalate. 



Since the equivalent number for oxalic acid is 4 - 5, there seems 

 no reason to hesitate about considering it as a compound of two 

 atoms carbon + three atoms oxygen ; for 



2 atoms carbon = 1'5 



3 atoms oxygen 3-0 



4-5 = oxalic acid. 

 Berzelius obtained the small quantity of hydrogen which he* 



