FORMIC ACID. 49 



Composition. In correspondence with the above formula, 100 

 parts of this acid must contain : 



Carbon 2 atoms .... 26*087 



Hydrogen 1 .... 2'174 



Oxygen 3 .... 52*174 



Water 1 .... 19-565 



100-000 



The atomic weight of the hypothetical anhydrous acid = 462'5 ; 

 its saturating capacity =2 1*62. According to the theory which we 

 have laid down, formic acid should be regarded as an oxalic acid 

 conjugated with hydrogen ==H.C 2 O 3 -J- HO ; but according to 

 ordinary views it is assumed to contain a radical /ontty/=C 2 Hj 

 which is believed to occur in several other combinations, as for 

 instance in chloroform. 



Combinations. The salts of formic acid are soluble; with 

 alkalies, it also forms acid salts. 



Formate of ammonia is known by its property of becoming 

 converted on heating into hydrocyanic acid (H 4 NO.C 2 HO 3 = 

 H.C 2 N + 4HO), and hence the hydrocyanic acid which often 

 appears during the decomposition of animal substances may be 

 dependent on the previous formation of formate of ammonia. 



There are certain combinations, which in reference to their 

 empirical composition, may be regarded as formic acid, but in 

 which the whole of the oxygen is replaced by chlorine, bromine, 

 iodine, or sulphur ; the best known of these is chloroform or per- 

 chloride offormyl, C 2 HC1 3 , which is employed in place of ether to 

 induce anaesthesia. 



Preparation. This acid was most commonly obtained in 

 former times by distilling a large quantity of ants with water or 

 spirit : from the distillate, which naturally only contained the acid 

 in a very dilute state, the concentrated acid was obtained according 

 to the ordinary methods by saturation with a base, and by the de- 

 composition of the crystallised salt with sulphuric acid. As, how- 

 ever, we have since ascertained that formic acid is a product of 

 the oxidation of many animal and vegetable substances, we are 

 now in the habit of obtaining it from various sources by the action 

 of oxidising agents, as peroxide of manganese and sulphuric acid, 

 chromic acid, or hypermanganic acid. It is best obtained by 

 adding a little water and sulphuric acid to a mixture of three parts 

 of sugar and one part of bichromate of potash (2 atoms of SO 3 

 to 1 atom of KO. 2CrO 3 ) and by distilling. 



Tests. This acid may be readily distinguished from most other 



