38 PHILOSOPHICAL TKAXSACTIOiVS. [aNNO 1776. 



Xl^. Easy Methods of Meastiring the Diminution of Bulk, lakiyig place on the 

 Mixture of Common Air and Nitrous Air ; tvitli Experiments on Flatina. 

 By John Ingenhousz, M.D., F. R.S. p. 257. 



Dr. I. having received from Abbe Fontanii a copy of a pamphlet, on the use 

 of some experiments for measuring the sakibrity of air, he imitated some of 

 them, and found them very useful for the intended purpose of measuring the 

 quantity of air absorbed or diminished by mixing the nitrous with the common 

 air ; by which criterion the degree of the salubrity of common air may be ascer- 

 tained according to the discovery of Dr. Priestley. Fontana first produces 

 nitrous air in a separate vessel, and then forces it into the glass, or other vessel, 

 in which it is to remain, till a communication be opened between this vessel and 

 the other which contains common air. Dr. I. found it a ditBcult matter to force 

 always just the same quantity of nitrous air into the vessel ; because he could 

 never be sure that the nitrous air had dislodged all the common air out ot it, or 

 had dislodged always the same quantity of common air. It this quantity is not 

 always just the same, some variety must happen in every experiment ; and thus 

 an exact valuation of the quantity of air absorbed cannot well be made. To 

 obviate in some measure this difficulty, and to abridge the experiment by mixing 

 suddenly the two airs together, he contrived a particular instrument. It is a 

 strong glass vessel, nearly 24- inches in diameter, and about as much in height : 

 a conical figure would perhaps be better. A brass cover, which embraces the 

 glass about half an inch ilownwards, is cemented to it, and has a hole in its 

 middle, corresponding with the hole in the glass vessel. This hole of the brass 

 cover has a female screw fitted to receive the male screw of a brass tube, about 

 7 inches long and about an inch in diameter, terminating at one end in a male 

 screw, and at the other, in a neck adapted to enter the mouth of an elastic 

 gum bottle, otherwise called boradchio or caout-chouc, to be tied to it with a 

 strong ribbon. This brass tube has towards each extremity an air tight cock, 

 by which the communication between one extremity and the other may be 

 opened or shut. Between these two cocks, about the middle ot the tube, is a 

 short lateral tube, communicating with the canal of the other tube. This 

 lateral tube has also an air tight cock, which opens or shuts up the communica- 

 tion with the long tube, and has a female screw to receive the male screw of 

 another short tube, which serves to recei\e a glass tube bent at right angles, 

 and of 2 feet or more in length ; the diameter somewhat more than that of a 

 large quill. This glass tube is to be divided into any number of equal parts. 



The instrument is used in the following manner. The elastic gum bottle 

 being well tied to tlie brass tube, all the cocks shut, and the glass tube fixed to 

 its place, he pours a certain quantity of aquafortis (v. g. § lb) into the glass 

 vessel, taking care that none of it touches the brass cover : he then puts into it 



