588 PHILOSOPHICAL TRANSACTIONS. [aNNO 1775. 



have wished; perhaps the difficulty in conducting the process, in the manner 

 proposed, has been, in some measure, the reason why so few experiments, on 

 this subject, have been made public. For though, in the hands of Dr. P., the 

 apparatus was sufficiently convenient, it must be confessed, that the conduct of 

 the process required more address, than generally falls to the share of those that 

 are unaccustomed to such experiments. Independent too of the inconveniencies 

 attending the process, there was another objection to the apparatus, which, with 

 most people, might have considerable weight. The bladder, which formed part 

 of it, was thought to render the water offensive ; and when the solvent power of 

 fixed air is considered, it will not appear improbable, that the water would be 

 always more or less tainted by the bladder. In some trials which Dr. N. made 

 with Dr. Priestley's apparatus, it always happened, that the water acquired a 

 urinous flavour; and this taste in the water was, in general, so predominant, 

 that it could not be swallowed, without some degree of reluctance. The diffi- 

 culty therefore in the conduct of the process, and the ofFensiveness of part of 

 the apparatus, made some less exceptionable method of producing the impreg- 

 nation desirable. This Dr. N. variously attempted, keeping convenience and 

 cleanliness constantly in view; and he flattered himself, that he had at last con- 

 trived an apparatus that would perfectly answer the intended purpose. Twelve 

 months had elapsed since this contrivance had been in constant use; and to that 

 time there was no reason to wish for the least alteration. Presuming therefore 

 on the possibility of its becoming, when known, extensively useful, and con- 

 vinced of the favourable reception which every attempt of this nature meets with 

 from the r. s., he begged leave to communicate a description of the apparatus 

 that he had invented, and of the manner of conducting the process. 



The apparatus is of glass, and consists of 3 vessels as a, b, c, fig. 1, 2, 3, 

 pi. 12. The glasses are accurately fitted to each other, and at the joints are 

 impervious both to air and water. The glass a is designed for the effervescing 

 substances. The vessel b is to contain the water to be impregnated with air. 

 In the lower part of the glass b is placed an ivory valve, surrounded with cork, 

 as in fig. 4. The cork a is fitted to the bottom of the glass b, and has through 

 it a hole, to receive the part b of the ivory valve. On the broader part of this 

 piece b, is placed a moveable piece c. The surfaces of these pieces are so 

 accurately ground, that, when applied to each other, no fluid whatever can pass 

 between them. The moveable part c is secured on the part b by the cover d, 

 which is so constructed, as to allow the piece c some motion, and this cover 

 has likewise holes to give passage to the air that shall raise the moveable piece c. 

 The glass c serves 2 purposes ; it confines the air on the surface of the water in 

 B, and at the same time prevents all danger of explosion by allowing the water 

 tq give place to the ascending air. 



