OP ARTS AND SCIENCES. 93 



VII. 



A METHOD OF OBTAINING AND OF MEASURING 

 VERY HIGH PRESSURES. 



By Carl Barus. 



Presented June 11, 1890. 



1. Historical. — Andrews's screw compressor has this advantage, that 

 the acting stress is brought to bear within the compass of the barrel. 

 In other arrangements, such, for instance, in which a cylindrical plunger 

 is forced into the barrel, stress must be exerted against the bedplate, 

 or applied in a way tending to flexure the plunger. The screw com- 

 pressor may therefore well be taken as the model of an apparatus of 

 greater strength and efficiency than was necessary in Andrews's work. 

 Indeed, Andrews himself seems to have been of this opinion,* and 

 toward the close of his life devised an apparatus of which screw 

 plungers are an essential part. Haunay and Hogarth,t however, were 

 the first to carry the practical improvement of the screw into execu- 

 tion. They reached pressures but slightly short of 900 atmospheres, 

 stating that their reasons for stopping work at this datum were quite 

 apart from the efficiency of their apparatus. With the screw com- 

 pressor X described below, I obtain above 2,000 atmospheres with 

 facility. §§ 17, 23. It is so constructed that a considerable volume 

 of liquid is operated on, admitting of a compression of five cubic inches 

 of volume decrement. Finally, special provision has been made for 

 the insulation of parts, thus enabling the observer to apply the essen- 

 tial electric methods § in studying his test samples. 



Particular notice should here be given of the remarkable modifica- 

 tion of Desgoffes's differential manometer, by which Amagat || succeeded 



* See Professor Everett's account in Nature, Vol. XXXIX. p. 556, 1889. 

 t Hannay and Hogarth^ Chem. News, Vol. XLI. p. 103, 1880. 



I It was made for me by tlie American Tool Co., No. 84 Kingston Street, 

 Boston, Benjamin J. Radford, Superintendent. 



§ I here have special reference to Tait's ingenious device. See Proc. Roy. 

 Sec. Ed., Vol. XIII. p. 2, 1884-85. Beiblatter, X. p. 149, 1886. 



II Amagat, C. R., Vol. CIII. p. 429, 1886. 



