694 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



greater number of tubes, and as tliey were heated by the steam inside of 

 them, they were more liable to contract and expand. Hall's tubes were 

 held by metallic rings; for these are now substituted India-rubber rings, 

 which expand or give way with the motion of the tube. To prevent cor- 

 rosion or galvanic action, he used copper tubes covered with a thin coating 

 of tin. The steam being allowed to escape into a large chamber, as in 

 the case where the water is within the tubes, there is evidently no loss by 

 back pressure for the want of space. Another advantage of this arrange- 

 ment is, that a water packing covers all joints, which might by leaking 

 endanger the vacuum. Mr. Sewell then answered various inquiries made 

 by Bartlett, Kowell, Root, and others, regarding structure and effect of 

 surface condensers. Mr. Stetson asked, for the purpose of satisfying those 

 who had read in some work of the action of heat upon water, after the air 

 had all been expelled from it, whether any diflerence between the action of 

 aerated water and of water deprived of air while in the boiling process, 

 had been observed. Mr. Sewell replied that none was noticed in connec- 

 tion with surface condensers. It was evident that a better vacuum could 

 be obtained than when the water was deprived of air. 



Mr. Garvey said there were three conditions to be observed in the boil- 

 ing of water. 1st. The atmospheric pressure. 2d. The hydrostatic pressure. 

 3d. The viscidity of the liquid. If the air is driven out of the liquid, its 

 particles are in closer relation, and a different condition arises; but all 

 these differences have but slight effect on the boiling point. 



As the time for adjournment had arrived before an opportuliity could be 

 given for the exhibition and explanation of other kinds of surface con- 

 densers, the same subject was selected for the next discussion. 

 '£ Adjourned, 



1 



American Institute Polytechnic Association, 

 February 25, 1864. 



Chairman, Prof. S. D. Tillman; Secretary, Mr. B. Garvey. 



Oil Analyzing Apparatus. 



An apparatus was exhibited for the analytical determination of coal oil, 

 petro-eum, &c., by fractional distillation, according to W. Regnault, the 

 distinguished French chemist. It consists of a cylindrical retort, made of 

 copper, of about 300 cubic centimeters capacity, provided with a tabu- 

 lature at the top for ifitroducing a thermometer, and a bent neck entering 

 into the tabulature of a condenser by a ground joint. The condenser has 

 an interior cylinder of brass, which terminates at the top and bottom in 

 narrow open tubes, the whole being fastened air-tight, in an outer cylinder 

 of the same metal. A continual current of cold water is poured into the 

 condenser through a funnel which opens near the bottom of the same. The 

 hot water is carried off by a tube at the top. The whole apparatus is sup- 

 ported by an iron tripod, at the base of which is an arrangement with five 

 glass cylinders, graduated into cubic centimeters, and standing in a row 

 on a movable support. 



The mode of operation is as follows: By means of a pipette, 100 cubic 



