374 Miscellanies. 



and transparent solution, the others left a residuum agreeable to the 

 gubstance mingled with the zinc. 



The author next ascertained by direct experiment, that the mixture 

 of acid and water which produces the most lively chemical action up- 

 on Zinc, is that which is the best conductor in a Voltaic apparatus ; 

 and also, that if to a cylinder of distilled zinc which (as before sta- 

 ted,) requires 1' 30" to yield a certain measure of gas, a platina wire 

 be attached, and immersed in the same fluid, an equal quantity is dis- 

 engaged in 30". Thus a cylinder of zinc having a fine platina wire 

 wrapped around it, or otherwise attached to it, affords a larger quanti- 

 ty of gas than a piece of isolated zinc. It seems therefore reasonable 

 to infer that in the production of hydrogen, by the zinc of commerce, 

 and diluted sulphuric acid, the water is decomposed by a galvanic ac- 

 tion. The zinc being positive, receives the oxygen, while the other 

 metal being negative, allows the hydrogen to escape in the gaseous 

 form, the quantity of which, in a given time, will depend on the en- 

 ergy of the electric current. 



Prof. De La Rive states that he finds in the zinc of commerce some 

 traces of tin, of lead, and a little more than 1 per cent of iron,* and 

 his experiments have proved that less than two per cent of iron 

 filings mingled with pure zinc, renders it as active with dilute acid, 

 as the zinc of commerce. 



The heat developed during the action of sulphuric acid on zinc is 

 generally in proportion to the rapidity of the evolution of gas, and 

 this, it is believed, arises also from the strength of the elqctric cur- 

 rent.— Si&. Univ. April, 1830. 



7. On the production of Formic Acid. — The fine discovery of Do- 

 bereiner, of the production of formic acid by the distillation of tar- 

 taric acid with sulphuric acid and the peroxide of manganese, is 

 known to chemists. It has since been obtained by other processes. 

 If a mixture be made of starch, peroxide of manganese, and diluted 

 sulphuric acid, and heated in a large retort, an effervescence will at 

 length take place, on account of the carbonic acid, and the mixture 

 will have acquired a decided odor of formic acid. By continuing 

 the distillation, formic acid will be obtained, accompanied by an 

 odoriferous principle, very irritating to the eyes, but which becomes 

 peparated by the saturation of the acid with the bases. 



Tunnerman, who first obtained formic acid by this process, took it 

 for a peculiar substance, l)ut Wohler shewed its real nature. Leibig, 



Prol. De La Planche finds also in the zinc of commerce a considerable portion of 

 {Cadmium. 



