OF ARTS AND SCIENCES. 63 



lime-water, carrying ■with it, of course, the products of the combustion 

 of the hydrogen. We first used, in order to absorb the carbonic acid 

 completely from the air in which the hydrogen burned, two cylinders 

 twenty-seven centimetres high and five centimetres in diameter, filled 

 with fragments of pumice-stone moistened with caustic potash ; not 

 satisfied with this large absorption surface, we next added to the 

 cylinders two Wolfe bottles containing a concentrated solution of caus- 

 tic potash, and finally substituted for the Wolfe bottles three five-bulb 

 potash-tubes. We repeatedly maintained a burning jet of hydrogen 

 in the globe for periods varying from four to six hours, with air 

 purified by passing through the three potash-tubes and two cylinders 

 described, and always obtained the same result ; viz, there was never 

 any perceptible cloud of carbonate of lime in the bottle containing 

 lime-water during the progress of the experiment, but after standing 

 twelve hours, an unmistakable deposit of crystalline carbonate of lime 

 was invariably found at the bottom of the lime-water. We might 

 have regarded this as sufficient evidence of the presence of an in- 

 finitesimal amount of carbon in the hydrogen, had we not found by 

 repeated trials, that the burning of the hydrogen had no influence 

 whatever on the formation of this crystalline deposit. 156,000 c. c. 

 of air (the contents of our aspirator), passed through the purifiers we 

 have described, still retained sufficient carbonic acid to produce a 

 deposit of crystalline carbonate of lime, when allowed time to separate 

 from the lime-water by crystallization.* In order to render the ex- 



* The fact that carbonate of lime may at first be dissolved by lime-water, has 

 been clearly shown by Vogel. (Schweigsrer's Journ. f. Ch. u. Phys., 1821, XXXIII. 

 207.) It is moreover very distinctly affirmed in the following passage from an 

 article, which has recently fallen under our notice, by Berthollet (Annates de 

 Chimie, 1789, III. 68) : — "I am indebted to M. Welter for an observation upon 

 the use of lime-water, which may be useful in cases where one wishes to de- 

 tect small quantities of carbonic acid. Lime-water has the property of dissolving 

 a little carbonate of lime, of which one can assure himself by blowing into it with a 

 tube ; the air expired produces a cloud which redissolves entirelj', until the lime- 

 water is saturated with the carbonate of lime which has been formed. If, there- 

 fore, it is desired to detect small quantities of carbonic acid by means of lime- 

 water, it is necessary to agitate some carbonate of lime with the latter, in order 

 that it may be saturated, before filtering it." That the carbonate of lime separates 

 after a time from the lime-water which had previously held it in solution, has also 

 been shown by one of us (Am. J. Sci., 1858, [2.] XXV. 42), — at that time 

 entirely ignorant of the experiments of Vogel and Welter. 



