474 PROCEEDINGS OF THE AMERICAN ACADEMY 



the space between c and d, about three or four inches in length, then filled 

 with a mixture of pure asbestos and peroxide of lead, and finally a plug of 

 asbestos is placed at d. As the sulphuric acid formed is to be absorbed 

 bj, and finally determined from, the pei'oxide of lead, — in order to ob- 

 viate the necessity of treating the whole of the asbestos in the tube to 

 obtain the sulphuric acid, which would be troublesome, and at the same 

 time preserve the asbestos packing in the posterior part of the tube in 

 a fit condition for future use, — it is important that the asbestos plug at 

 c should be packed closely enough to prevent any particles of the perox- 

 ide of lead from passing back of this plug. 



As already stated, the object of mixing asbestos with the peroxide of 

 lead is to prevent the formation of a channel along the top. In this 

 manner but a short column of the mixture of asbestos and peroxide of 

 lead will suffice to secure complete conversion of the sulphurous acid. 

 The combustion is conducted precisely as for the determination of car- 

 bon and hydrogen alone, except that the portion of the tube which con- 

 tains the peroxide of lead is maintained at a gentle heat, sufficient to 

 prevent condensation of water in that part of the tube and at the cork, 

 but avoiding a temperature which would decompose the peroxide of 

 lead. As usual, the water formed is absorbed in a chloride of cal- 

 cium tube, and the carbonic acid in Liebig's potash bulbs with a mulder 

 tube attached. 



After the close of the combustion, when the tube shall have sufficiently 

 cooled it is carefully removed from the furnace, the mixture of peroxide 



will be seen that the liability to the formation of a channel is obviated in my pro- 

 cess by mixing the peroxide of lead with a large proportion of asbestos. The 

 asbestos serves also to increase the porosity of the mass, and in this manner also 

 to lessen the chances of escape of sulphurous acid without coming in contact with 

 the peroxide. I may here add that, in making the combustion with oxygen in 

 presence of asbestos, the quantity of sulphurous acid which reaches the peroxide 

 of lead is by no means very large. In a preliminary experiment in which carbonate 

 of soda was employed instead of peroxide of lead, (the substance burnt being bi- 

 sulphide of carbon,) the carbonate of soda was found to contain witliin about 9 per 

 cent of the equivalent quantity of sulphur; and a portion of the deficiency it is ncit 

 unlikely may have been taken up by the impure asbestos that was employed in this 

 instance. 



Concerning the other source of error in the determination of carbon which 

 Carius mentions, it will suffice to remark that, in my process, the peroxide of lead 

 is kept at so high a temperature that the absorption of carbonic acid appears to 

 be prevented. 



