DISCOURSE OF ^y. B. TAYLOII. 329 



Sulphurie-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 

 18J feet) gave correspondingly enlarged and sensitive indications. 

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

 by Daniell 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 



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



