156 DR. FARADAY ON THE LIQUEFACTION AND SOLIDIFICATION OF 



The condensing tubes were of green bottle glass, being from Jth to Jth of an inch 

 external diameter, and from ^^-6 to ^th of an inch in thickness. They were chiefly 

 of two kinds, about eleven and nine inches in length ; the one, when horizontal, 

 having a curve downward near one end to dip into a cold bath, and the other, being 

 in form like an inverted siphon, could have the bend cooled also in the same manner 

 when necessary. Into the straight part of the horizontal tube, and the longest leg of 

 the siphon tube, pressure gauges were introduced when required. 



Fig. I. 



Fig. 2. 



iir o 



Caps, stop-cocks and connecting pieces were employed to attach the glass tubes to 

 the pumps, and these, being of brass, were of the usual character of those employed 

 for operations with gas, except that they were small and carefully made. The caps 

 were of such size that the ends of the glass tubes entered freely into them, and had 

 rings or a female screw worm cut in the interior, against which the cement was to 

 adhere. The ends of the glass tubes were roughened by a file, and when a cap was to 

 be fastened on, both it and the end of the tube were made so warm that the cement*, 

 when applied, was thoroughly melted in contact with these parts, before the tube and 

 cap were brought together and finally adjusted to each other. These junctions bore 

 a pressure of thirty, forty, and fifty atmospheres, with only one failure, in above one 

 hundred instances ; and that produced no complete separation of parts, but simply a 

 small leak. 



The caps, stop-cocks, and connectors, screwed one into the other, having one com- 

 mon 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 stop-cocks. All these screw 

 joints were made tight by leaden washers ; and by having these of different thickness, 

 equal to from f th to -g-th 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. 



* Five parts of resin, one part of yellow bees'-wax, and one part of red ochre, by weight, melted together. 



