Apparatus for use in Gas-analysis. 535 



the amount of change suffered by the lime- or baryta-water. 

 Sometimes the amount of the insoluble carbonate is weighed, 

 and sometimes the diminution of alkalinity is noted ; and the 

 characteristic of this method is that the point to be observed 

 is the change in the reagent, and not in the volume of the gas. 



In carrying out these measurements of the carbonic acid in 

 the air the manipulation is of the simplest description. The 

 air is contained in a large stoppered flask or bottle, the capa- 

 city of which has been measured. The stopper is taken out, 

 the baryta-water is poured in, and the stopper is replaced. 

 Then the bottle is shaken up for a sufficient length of time; 

 and ultimately the operator takes the stopper out, and deals 

 with the carbonate of baryta or the baryta-water in the well- 

 known manner. 



Now let us suppose that the chemist had to measure the 

 carbonic acid in a gas lighter than air. He has his bottle 

 filled with, for example, coal-gas. 



It will be apparent that when he tries to pour the baryta- 

 water into the gas he will meet with difficulties. If the 

 mouth of the bottle be held upwards, the gas will escape when 

 the stopper is removed : and, if the mouth be directed down- 

 wards, the operator will not be able to pour the baryta-water 

 into the bottle. 



Our new apparatus is designed to enable the operator to 

 overcome this difficulty. We make the stopper hollow, and 

 place the reagent in the stopper. Instead of a solid stopper 

 we use a flask of thick glass, the neck of which is ground so 

 as to fit into the neck of the gas-bottle. 



The following examples will serve to illustrate our method 

 of operating : — 



We had occasion to measure the carbonic acid, sulphu- 

 retted hydrogen, and ammonia in crude coal-gas — that is to 

 say, in coal-gas from which the tar and water distilling with 

 the tar had been removed, but which had not been further 

 purified. 



The gas in question was collected by displacement in a 

 bottle holding 2750 cubic centim. ; and about 50 cubic centim. 

 of strong baryta-water was placed in the little flask which 

 was employed instead of a stopper to close the bottle con- 

 taining the gas. The apparatus was then shaken, and the 

 resulting carbonate of baryta collected on a filter, washed, 

 ignited, and weighed. From the amount of carbonate the 

 amount of carbonic acid was calculated. In another experi- 

 ment the sulphuretted hydrogen was measured by using a 

 solution of acetate of lead, the sulphuret of lead being subse- 

 quently converted into sulphate of lead, and weighed. In a 



