170 An Account of some Experiments on the 



hydrogen irifJicates an absorption of oxygen by the tia 

 equivalent to eight cubic inches, or (as 100 cubic inches 

 weigh 34-2 grains) to 2*736 grains, the protoxide of tin 

 appears to contain 1 1'QQ per cent, of oxyoen. 



These analyses of the oxides, compared with those of the 

 combinations of tin and chlorine, are found very nearly to 

 agree. The ratio of oxygen to chlorine in the two first 

 similar connpounds, the tin being as A5, is as 7'3 to 3J-4 ; 

 and in the two last, viz. the peroxide and the liquor of 

 Libavius, as 7'6 to 33-5, or as 15-2 to 67. 



As the black oxide of iron is formed bv the decomposi- 

 tion of ferrane by a solution of potash, and the red oxide 

 by that of ferranea, it is evident that these oxides and com- 

 binations of iron and chlorine should coincide in the pro- 

 portions of their constituent parts. This appears from the 

 analyses* of Dr. Thomson to be nearly the case; for iron 

 being as 29'5, the oxygen is to the chlorine in the black 

 oxide and ferrane as 8 instead of 7*5 to 33 6 ; and in the 

 two others as 8 to 33-6, or as 132 to 53'5. Here the agree- 

 ment is less than in other instances; I ut this is not sur- 

 prising considering the diflTereiit estimates of the propor- 

 tions of oxygen in the oxides of iron, and the difficulty of 

 ascertaining them correctly. 



The yellow oxide of lead and the white oxides of anti- 

 mony, bismuth, zinc, and arsenic are formed, when the 

 combinations of these metals and chlorine are decomposed 

 by a solution of potash. But on comparison with the best 

 analyses of the oxide?, there is not, excepting in the case 

 of zinc and arsenic, that coincidence of proportions which 

 might be expected. Zinc being as 34-.5, the oxygen in the 

 oxide, from the analysis of Proust, is to the chlorine as 

 7*5 to 344 ; and the arsenic being as 21*9, the oxygen, 

 from the analysis of the same chemist, is to the chlorine as 

 73 to 33*6. The analyses of the oxides nf the other metals 

 being at variance with ihose of the chlorine combinations, 

 I was induced to make the following experiments, with the 

 hope of discovering the cause of the ditllrence. 



100 grains ol lead, which had been precipitated from the 

 nitrat of lead by zinc, were dissolved in nitric acid and 

 thrown down by carbonal of potash. This precipitate of 

 carbonat of lead was well washed, and dried and heated to 

 dull redness for a quarter of an hour in a platina crucible; 

 by this treatment all the carbonic acid was expelled ; the 

 remaining yellow oxide weighed 107"7 grains, and it dis- 



• Nicholson's Journal, vol. xxvii. p. S75. 



solved 



