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Messrs. J. B. Harmay and J. Hogarth. [Feb. 26, 



gaseous state. The property of dissolving -solids being supposed 

 peculiar to liquids, it seemed to us that on passing through the critical 

 state there would be a precipitation of solid, or if on the other hand 

 no separation occurred, a further proof of the perfect continuity of 

 the gaseous and liquid states would be presented. To put the matter 

 to the test, a solution of potassic iodide in alcohol was prepared, and 

 a strong tube filled to about one-half with the solution. After sealing, 

 the tube was placed in an air-bath, and heat applied. No precipita- 

 tion of solid could be seen even at a temperature of 350° C, more 

 than 100° C. above the critical point of alcohol. 



For the examination of the phenomena of solution some form of 

 pressure apparatus was necessary, so that the volume of the fluid 

 experimented on might be altered at pleasure. After several experi- 

 ments we adopted a modified form of Dr. Andrews' apparatus, which 

 allowed us to change an experimental tube in a few minutes, and 

 showed no sign of leakage at the highest pressure reached (fig. 4). A 

 section of the apparatus is shown in the annexed engraving. It is made 

 of wrought iron tubing such as is used in hydraulic machinery, about 

 \ inch internal, and 1 inch external diameter. The length of the 

 apparatus is 9 inches, and there is a side tube welded on, measuring 

 about 3 inches, for the insertion of the manometer tube. On the 

 ends of the tube are screwed strong caps, also of wrought iron ; 

 Through one of these the pressure screw works, the others serve for 

 the admission of the experimental and manometer tubes. The dis- 

 tinguishing feature of the apparatus is the packing for the screw and 

 tubes. It consists of a solid plug of india-rubber, about ^ inch thick, 

 placed in the hollow cap, so that it serves both for packing the screw 

 or tube, and for making the joint between the cap and the iron tube 

 tight. To prevent the pressure screw from cutting the india-rubber, 

 a lining of thin leather, well soaked in lard, was placed between it 

 and the rubber. The tubes were similarly packed, and to keep them 

 from being forced out through the aperture in the cap, a thickening 

 was made in the glass by fusing and pressing together, and between 

 this bulbous part and the iron a strong leather washer was placed. 

 In some cases, when a very high pressure was wanted, the tube was 

 cemented in with oxy chloride of zinc, which effectually prevented it 

 from coming in contact with the iron cap. With this mode of 

 packing the pressure screw did not require to be very fine, the one 

 commonly used being ± inch in diameter and screwed 30 threads to 

 the inch. The only limit to the pressure was the frailty of the glass 

 tubes ; we have, however, attained a pressure of 880 atmospheres as 

 shown by an air manometer, and even at this enormous pressure the 

 screw could be freely moved in either direction without leakage. The 

 apparatus was as tight with mercury as with water, so that there was 

 no necessity for using two liquids as in Dr. Andrews' machine. When 



