98 Composition of inorganic Bodies. [Feb. 



and the matrass weighed. The barometer varied during the 

 experiment between 24*6 and 24-7. 



1 continued these experiments for three days, making three 

 each day. The weight of the sulphurous acid varied from 1-308 

 to 1-311, without it being possible to ascribe this variation to 

 changes in the pressure of the atmosphere. The quantity of air 

 which the air-pump extracted from the matrass weighed 0-576 

 to 0-578 gramme ; but when the air was allowed to enter 

 through a tube filled with muriate of lime, it always weighed 

 0-583 gramme. At each experiment, the matrass was weighed 

 after being exhausted, to be sure that the air-pump had always 

 extracted the same quantity of air. The stop-cock was examined 

 each day by leaving the exhausted matrass for half an hour on 

 the balance without its weight increasing by the entrance of air. 

 The errors of observation in this experiment ought always to 

 have a tendency to give the specific gravity of the gas too small, 

 in consequence of a mixture of air with the sulphurous acid gas. 

 Only a single circumstance could contribute to increase the 

 weight. The grease upon the stop-cock might have absorbed a 

 small quantity of sulphurous acid. To determine this point, I 

 weighed the stop-cock before and after each experiment ; but 

 its weight was not altered. It is possible likewise that a httle 

 sulphuric acid might evaporate, and remain suspended in the 

 gas ; but I always left the gas a long time standing on the 

 mercury before putting it into the matrass ; so that the vapour, 

 supposing it to exist, had all the time necessary to be deposited. 

 If we admit 1-31 as the weight of the sulphurous acid gas ia 

 the preceding experiments, 58-3 : 131 :: 1-00 : 2-247. If in these 

 2-247 parts of sulphurous acid there is an equal volume of oxy- 

 gen whose weight is 1-10359, 100 parts of sulphur are combined 

 with 96-62 parts of oxygen instead of 98-954, as follows from the 

 analysis of sulphuric acid. This deviation is too great to be 

 merely an error of observation. Hitherto all circumstances 

 speak in favour of the results drawn from the analysis of sulphuric 

 acid, which agree so well with the experiments on the composi- 

 tion of the sulphurets, and which agree exactly with the analyses 

 of other saline combinations, as we shall immediately see. 



I have not been able to find the cause of this anomaly. Some 

 chemists pretend that oxygen gas, when it unites with sulphur, 

 diminishes in volume. This diminution has been supposed to go 

 as far as y^th. But whether it is owing to a small quantity of 

 hydrogen in the sulphur, or constitutes an exception to what we 

 consider as a general law, remains to be determined. 



(To be continued.) 



