BODIES GENERALLY EXISTING AS GASES. 159 



The arrangement by which this cooling power was combined in its effect on gases 

 with the pressure of the pumps, was very simple in principle. An air-pump receiver 

 open at the top was employed ; the brass plate which closed the aperture had a small 

 brass tube about six inches long, passing through it air-tight by means of a stufSng- 

 box, so as to move easily up and down in a vertical direction. One of the glass con- 

 densing siphon tubes, already described, fig. 1, was screwed on to the lower end of 

 the sliding tube, and the upper end of the latter was connected with a communi- 

 cating tube in two lengths, reaching from it to the condensing pumps ; this tube was 

 small, of brass, and Qj feet in length ; it passed six inches horizontally from the 

 condensing pumps, then rose vertically for two feet, afterwards proceeded horizontally 

 for seven feet, and finally turned down and was immediately connected with the 

 sliding tube. By this means the latter could be raised and lowered vertically, 

 without any strain upon the connexions, and the condensing tube lowered into the 

 cold bath in vacuo, or raised to have its contents examined at pleasure. The capa- 

 city of the connecting tubes beyond the last condensing pump was only two cubic 

 inches. 



When experimenting with any particular gas, the apparatus was put together fast 

 and tight, except the solid terminal screw-plug at the short end of the condensing 

 tube, which being the very extremity of the apparatus, was left a little loose. Then, 

 by the condensing pumps, abundance of gas was passed through the apparatus to 

 sweep out every portion of air, after which the terminal plug was screwed up, the 

 cold bath arranged, and the combined effects of cold and pressure brought to unite 

 upon the gas. 



There are many gases which condense at less than the pressure of one atmosphere 

 when submitted to the cold of a carbonic acid bath in air (which latter can upon 

 occasions be brought considerably below —106° Fahr.). These it was easy, therefore, 

 to reduce, by sending them through small conducting tubes into tubular receivers 

 placed in the cold bath. When the receivers had previously been softened in a spirit 

 lamp flame, and narrow necks formed on them, it was not difficult by a little further 

 management, hermetically to seal up these substances in their condensed state. In 

 this manner chlorine, cyanogen, ammonia, sulphuretted hydrogen, arseniuretted hy- 

 drogen, hydriodic acid, hydrobromic acid, and even carbonic acid, were obtained, 

 sealed up in tubes in the liquid state; and euchlorine was also secured in a tube 

 receiver with a cap and screw-plug. By using a carbonic acid bath, first cooled in 

 vacuo, there is no doubt other condensed gases could be secured in the same way. 



The fluid carbonic acid was supplied to me by Mr. Addams, in his perfect apparatus, 

 in portions of about 220 cubic inches each. The solid carbonic acid, when produced 

 from it, was preserved in a glass ; itself retained in the middle of three concentric 

 glass jars, separated from each other by dry jackets of woollen cloth. So eflfectual 

 was this arrangement, that I have frequently worked for a whole day of twelve and 

 fourteen hours, having solid carbonic acid in the reservoir, and enough for all 



