DISCOURSE OF W. B. TAYL.OK. 329 



Sulphuric-acid Barometer. In 1856, Henry had constructed for 

 the Smithsonian Institution, at the suggestion of Professor George 

 C. Schaeffer, a large sulphuric-acid barometer, whose column being 

 more than seven times the height of the mercurial column (about 

 18 J feet) gave correspondingly enlarged and sensitive indications. 

 Water barometers with cisterns protected by oil, (as that constructed 

 by Daniel 1 for the Royal Society,) have always proved instable. 

 With reference to sulphuric acid, "The advantages of this liquid 

 are: 1st that it gives off no appreciable vapor at any atmospheric 

 temperature ; and 2nd that it does not absorb or transmit air. The 

 objections to its use are: 1st the liability to accident from the cor- 

 rosive nature of the liquid, either in the filling of the tube or in its 

 subsequent breakage; and 2nd its affinity for moisture, which tends 

 to produce a change in specific gravity." The latter defect was 

 obviated by a drying apparatus consisting of a tubulated bottle con- 

 taining chloride of calcium, and connected by a tube with the glass 

 bottle forming the reservoir, which excluded all moisture from 

 the transmitted air. "The glass tube [of the barometer] is two 

 hundred and forty inches long, and three-fourths of an inch in 

 diameter; and is inclosed in a cylindrical brass case of the same 

 length, and two and a half inches in diameter. The glass tube is 

 secured in the axis of the brass case by a number of cork collars, 

 placed at intervals." * This barometer continued in successful and 

 satisfactory use for many years; and had its readings constantly 

 recorded. 



Of several of Henry's courses of experiments, no details have 

 been published ; and his original notes appear to have perished. 

 In 1861, he made a number of experiments on the effects of burn- 

 ing gunpowder in a vacuum, as well as in different gases. 



"A series of researches was also commenced, to determine more 

 accurately than has yet been done, the expansion produced in a bar 

 of iron at the moment of magnetization of the metal by means of 

 a galvanic current. The opportunity was taken with the consent 

 of Professor Bache, of making these experiments with the delicate 

 instruments which had previously been employed in determining 



* Proceed. Am. Assoc. Albany, Aug. 1856, pp. 135-138. 



