406 Dr. Tlwmson on [June, 



Oxygen 5'775 cubic inches. 



Azote 21-725 



27-500 



The next step was to determine the purity of the oxygen gas 

 obtained from the bleaching powder. This was easily done by 

 mixing a measured quantity of it with hydrogen gas, burning the 

 mixture by means of an electric spark, and noting the diminution 

 of bulk. One-third of this diminution denotes the volume of 

 oxygen gas present in the mixture before the combustion. By 

 this method, I ascertained the proportions of oxygen and azote 

 that existed in my gas. I may state the results. The gas was 

 received in three jars of unequal sizes. The gas in these three 

 jars was composed as follows : 



First jar 83^ oxygen + 16|- azote. 



Second jar ... . 91-6 + 8-4 



Third jar 93-l + 6> 



Knowing the volume of gas in each jar, it was easy to deter- 

 mine the absolute quantity of azotic gas present. It amounted 

 to 42-05 cubic inches. Deducting the 21-725 cubic inches 

 which existed in the common air of the retort driven off by heat, 

 there rem^iined a surplus of 20-33 cubic inches of azote. 



A very simple consideration of the phenomena of the process 

 will enable us to account for this surplus of azotic gas. The 

 extrication of the oxygen gas from the bleaching powder lasted 

 four hours. It was accompanied by the extrication of 755"98 

 grains of water, which came off chiefly, if not entirely, during the 

 first hour, and it was totally converted into steam. JVow 755-98 

 grains of water are very nearly 2-98 cubic inches ; and when 

 water is converted into steam, its bulk increases about 1700 

 times ; so that the bulk of the steam from this quantity of water 

 would be 5066 cubic inches. All this quantity would pass 

 successively through the retort : the consequence would be that 

 a much greater proportion of the common air of the retort would 

 pass into the receiver than would have been driven out by the 

 simple expansion caused by the heat; this air in the retort 

 being replaced by the steam ; but after the steam ceased to form, 

 it would be driven out of the retort in its turn by the oxygen gas 

 that still continued to be evolved; so that ultimately the retort 

 would contain only pure oxygeii gas expanded to the degree 

 produced by the heat to which the retort was exposed. That 

 this was really the case was obvious from this circumstance. 

 After the retort was allowed to cool, it was found perfectly dry ; 

 of consequence, all the steam had been driven out of it. The 

 surplus of azote then found in the gas had been driven out of the 

 retort by the steam, and its place in the retort had been uiti- 



