402 ZINC, CADMIUM, LEAD, c. 



be poured at once into a glass vessel containing 

 as much caustic potash or soda as will saturate 

 the whole muriatic acid in combination with the 

 protoxide. A black powder falls, which is prot- 

 oxide of tin ; it may be separated by a filter, edul- 

 corated and dried. When in combination with 

 acids, this oxide has a great tendency to combine 

 with more oxygen, and to be converted into 

 peroxide ; but when in a separate state, and 

 dry, I have kept it for years in a common phial, 

 without observing any alteration in its colour. 



The peroxide of tin has a yellowish colour. 

 It may be obtained by digesting tin in nitric 

 acid, and gradually raising the temperature to 

 redness. The acid is decomposed and driven 

 off, while the peroxide of tin remains behind in 

 a state of purity. 



Both of these oxides form salts with muriatic 

 acid ; but my attempts to determine the atomic 

 weight of tin, by a rigid analysis of these salts, 

 did not succeed. The following experiment, 

 however, which I have several times repeated, 

 gives the composition of peroxide of tin, from 

 which it is easy to deduce the atomic weight of 

 this metal. 



Atom of 7*25 grains of pure tin were put into a plati- 

 num crucible, and dissolved in a sufficient quan- 

 tity of very dilute nitric acid. The solution was 

 slowly evaporated to dryness, and the crucible 

 gradually raised to a red heat. The peroxide of 



