1835.] Improvements in Science. 125 



of formic acid may be judged of by the volume of carbonic 

 acid disengaged, when a liquid containing formic acid is 

 heated with red oxide of mercury. The carbonic acid 

 should be collected and estimated in a proper apparatus. 



When formic acid is combined with bases, it is necessary 

 to add, besides the red oxide of mercury, some acetic acid 

 to set the formic acid at liberty. 



3. The formates of zinc, copper, cadmium, bismuth, lead, 

 nickel, uranium, cerium, and cobalt, when exposed to a red 

 heat in a glass tube over a spirit lamp, are decomposed and 

 their oxides are completely reduced. If the flame of the 

 blowpipe is directed upon the more difficultly fusible metals, 

 while in the tube they appear through the glass to possess 

 the metallic lustre peculiar to them. The employment of 

 formic acid for procuring the rare metals, is to be preferred 

 to hydrogen, and as the price of formic acid is low, it is to 

 be hoped that the reduction will be speedily made on a great 

 scale. 



4. Formic acid may also be used to determine the quan- 

 tity of oxygen contained in the peroxides. For this purpose 

 a determinate quantity of the peroxide is heated with formic 

 acid. The gas disengaged, which is a mixture of carbonic 

 acid and common air, should be collected, and the quantity 

 of carbonic acid determined by means of caustic potash 

 noting the barometric pressure, the temperature and mois- 

 ture, and by dividing the volume of the acid by 2, the 

 quotient expresses the volume of oxygen taken from the 

 peroxide. Its weight is then calculated. 



5. The method recommended by Dobereiner of preparing 

 formic acid with sugar, is a very good one. The acid thus 

 obtained always contains some acetic acid, which is de- 

 tected when it is treated with red oxide of mercury. The 

 acetic acid may be separated by employing instead of chalk, 

 as recommended by Dbbereiner, carbonate of lead, to satu- 

 rate with the assistance of heat ; the acid liquid passing over 

 in distillation, and separating by crystallization the formate 

 of lead which is less soluble than the acetate, which dis- 

 solves easily. The formate is distilled with sulphuric acid 

 previously diluted with its weight of water, and pure con- 

 centrated formic acid is thus obtained possessing an acid 

 and agreeable odour. 



