98 On the Liquefaction and Solidification [1844* 



other, having one common screw thread, so as to be combined 

 in any necessary manner. There were also screw plugs, some 

 solid, with a male screw to close the openings or ends of caps, 

 &c., others with a female screw to cover and close the ends of 

 stopcocks. All these screw joints were made tight by leaden 

 washers ; and by having these of different thickness, equal to 

 from ^ths to ^-ths of the distance between one turn of the screw 

 thread and the next, it was easy at once to select the washer 

 which should allow a sufficient compression in screwing up to 

 make all air-tight, and also bring every part of the apparatus 

 into its right position. 



I have often put a pressure of fifty atmospheres into these 

 tubes, and have had no accident or failure (except the one 

 mentioned). With the assistance of Mr. Addams I have tried 

 their strength by a hydrostatic press, and obtained the following 

 results : A tube having an external diameter of 0*24 of an 

 inch and a thickness of 0*0175 of an inch, burst with a pressure 

 of sixty-seven atmospheres, reckoning one atmosphere as 15 Ibs. 

 on the square inch. A tube which had been used, of the shape 

 of fig. 1, its external diameter being 0*225 of an inch, and its 

 thickness about 0*03 of an inch, sustained a pressure of 118 

 atmospheres without breaking, or any failure of the caps or 

 cement, and was then removed for further use. 



A tube such as I have employed for generating gases under 

 pressure, having an external diameter of 0*6 of an inch, and a 

 thickness of 0*035 of an inch, burst at twenty-five atmospheres. 



Having these data, it was easy to select tubes abundantly 

 sufficient in strength to sustain any force which was likely to 

 be exerted within them in any given experiment. 



The gauge used to estimate the degree of pressure to which 

 the gas within the condensing tube was subjected was of the 

 same kind as those formerly described *, being a small tube of 

 glass closed at one end with a cylinder of mercury moving in 

 it. So the expression of ten or twenty atmospheres, means a 

 force which is able to compress a given portion of air into y^th 

 or ^th of its bulk at the pressure of one atmosphere of 30 

 inches of mercury. These gauges had their graduation marked 

 on them with a black varnish, and also with Indian ink : there 

 are several of the gases which, when condensed, cause the var- 

 * Philosophical Transactions, 1823, p. 192; see also p,91, 



