148 Intelligence and Miscellaneous Articles. 



the sound of a pistol-shot; but the splinters of broken glass were 

 not thrown about, owing to the metal cover. 



In order to investigate Mariotte's law under high pressures, I 

 employ a cylindrical glass tube capable of containing 40 to 50 cubic 

 centims. of gas ; a capillary glass tube is welded to this reservoir, in 

 which the compressed gases will be measured. The other extremity 

 of the reservoir is open and tapered. This apparatus is filled with 

 the gas to be examined pure and dry, the extremity of the capillary 

 tube is welded, and to the lower point a kind of small inverted gauge 

 filled with mercury is fitted, which admits of the apparatus being 

 placed in the laboratory-tube filled with mercury. At the moment 

 when the pressure is exerted by the machine, the mercury, pressed 

 by the water, will penetrate into the reservoir through the tapered 

 part, will drive back the gases in the capillary tube, and will just 

 stop at a point of its height. In order to determine this point exactly 

 (which cannot be done during the experiment, because the apparatus 

 is enclosed in the steel tube), I had recourse to an artifice which 

 gives extremely correct results. 



With this object I slightly gilded the interior of the capillary tube 

 by M . Bbttger's process. The mercury, rising in contact with the sides, 

 dissolves the gold ; and the height of the bright metal corresponds 

 exactly with the height attained by the mercury. This is noted on 

 a coat of varnish applied to the surface of the glass. It can be un- 

 derstood how a great number of heights, corresponding to the vo- 

 lumes occupied by the gas at pressures determined by the manometer, 

 may thus be found. 



The correctness of the determinations which I have obtained de- 

 pend especially (1) on the marking of the heights attained by the 

 mercury in the capillary tube, (2) on the weights of this mercury, 

 (3) on the correctness of the manometer. I have assured myself by 

 numerous experiments that the volume of the mercury could be ob- 

 tained very correctly ; the weight taken has always been the mean 

 of four operations. I have already discussed the correctness of the 

 manometer; I have moreover compressed at the same time, in the 

 same tube, two different gases. I thus proved that the volumes occu- 

 pied by the two gases under identical pressures corresponded well to 

 the numbers found in my experiments. The numbers obtained have 

 not undergone the correction due to the compressibility of the glass 

 apparatus ; I did not know this contraction ; I made all my de- 

 terminations for the different gases under the same pressures, in such 

 a manner that, if a cause of error not recognized should vitiate my 

 results by the same quantity, the experiments, made under identical 

 conditions, will still remain comparable. 



As M. Regnault has done in his memorable researches on the com- 

 pressibility of gases, I have calculated the departures from Mariotte's 



VP 



law by employing the formula — — ^ ; the numbers thus obtained were 



taken as lengths of the ordinates for the construction of the curves, 

 which cannot be given here : — 



