I 



Dr. Andi-ews on a new Aspirator. 331 



of air at a standard temperature and pressure which has passed 

 through the apparatus. If the aspirator be applied to the deter- 

 mination of the amount of aqueous vapour, or other absorbabla 

 constituent in the atmosphere, it \nll be necessary to find also 

 the mean temperature and pressure of the air during the course 

 of the experiment. With these data, a simple calculation \nll 

 give the exact weight or volume of the aqueous vapour in the air. 



It is unnecessaiy to point out the many applications which an 

 aspirator aifording an absolutely uniform current of air may 

 receive. In the chemical laboi'atory it will frequently be found 

 a very convenient instniment of research, and may even be ap- 

 plied in some cases to quantitative experiments. But it is 

 chiefly in atmospheric inquiries that this aspirator v.ill find its 

 applications ; and in the deteimination of the amount of oxygen, 

 carbonic acid, aqueous vapom', and even ammonia in the air, it 

 will prove, if I am not mistaken, a usefid addition to the meteoro- 

 logical obsei"vatory. For these various objects its size and form 

 will requu'e to be modified ; and it will be necessaiy where large 

 quantities of air are operated on, to enlarge considerably its di- 

 mensions and employ more powerful clock-machinery than I 

 have found necessary. 



The capacity of A in the apparatus I employed was 21'633 

 litres, or nearly 1320 cubic inches. With a pendulum of the 

 ordinary length, six hours were required for its ascent; but by 

 reducing the length of the pendulum, the same operation was 

 completed in an hour and a half. In the latter case, a current 

 of air at the rate of 240 cent. cub. (14"6 cub. in.) per minute 

 passed through the apparatus, and under these conditions I made 

 a few experiments on the relative desiccating powers of certain 

 substances, the results of which I will now very briefly state. 



With carefully dried gj^psum in T, and fragments of pumice 

 moistened with sulphuric acid in T', the latter underwent no 

 change of weight after the passage of the first mcasm-e of the 

 aspirator ; but in the next experiment (the same tubes being 

 employed) it gained 0'056 grm. {0'86 grain) ; and in a subse- 

 quent trial, after two hours had been allowed to elapse in order 

 to allow the moisture to be imbibed bv the gypsum, there was 

 still a gain of 0-03 1 grm. (0-52 gr.). 



With fused cMoride of calciimi in T, and sulphuric acid in T', 

 the gains of T' in three consecutive experiments were respectively 

 0-033, 0-040, and Q-OIO grm. 



Dry sulphate of lime appears therefore to be superior to fused 

 chloride of calcium, but neither desiccates the air with sufficient 

 energy to be employed in these experiments. 



With sulphuric acid in T as well as in T', the latter cx])cri- 

 enccd no change of weight till sixteen measm-cs of the aspirator 



