566 



NATURE 



[Oct. 9, 1879 



introduced before the heating, to allow it to be taken for granted 

 that during the experiment there was no residual air.i Another 

 method of Regnault's was to have two iron bottles of as nearly 

 as possible the same size cast in one piece. In one of these the 

 substance was placed, and in the other a small quantity of 

 mercury. The necks were then partially closed by loose stoppers, 

 and the system was heated in a muffle. After heating it was 

 withdrawn and allowed to cool, and the quantities remaining in 

 the bottles were determined by suitable means. 

 ' Grabowski,^ in 1866, did much to shorten the Dumas calcula- 

 tion, while he allowed the method to retain all its accuracy and 

 simplicity when he proposed to heat a bulb containing air in 

 the same bath and of the same size as that containing the sub- 

 stance. After being heated the two bulbs were then sealed at 

 the same temperature. Bunsen,^ in 1867, employed an air-bath 

 similar in principle to those of Mitscherlich and Regnault, but 

 heated it by a very elaborate arrangement of gas-burners. He 

 also simplified the calculation by taking care that all the tubes 

 were of exactly the same weight and same size. He did not 

 seal the tubes, but closed them by glass caps lined with india- 

 rubber and fitted with glass plugs. Dumas,* in cases where the 

 vapour rendered the outlet difficult to seal, used globes fitted 

 with ground stoppers. 



Forthe Dumas processat high temperatures Deville and Troost,* 

 in 1857-9, recommended heating the bulb in a specially constructed 

 furnace in the vaponrs of substances having high but definite 

 boiling-points, such as mercury, sulphur, zinc, or cadmium (in 

 1873 Dewar and Dittmar' used a bath of boiling zinc in experi- 

 ments on the vapour-density of potassium) ; for temperatures 

 above the boiling-point of sulphur they used porcelain globes. 

 For ^ temperatures up to that point the smaller and more compact 

 apparatus devised by Greville Williams answers admirably. 



Roscoe,' last year, in determining the vapour densities of the 

 chloride of lead and thallium, used porcelain globes of 300 c.c. 

 capacity, heated in a muffle, but determined the temperature by 

 the method of specific heat, a large piece of platinum being 

 employed for the purpose, and checked the resiilt by the simul- 

 taneous determination of the vapour-density of mercury. 



For' working at a reduced pressure Regnault proposed 

 partially exhausting the bulb by means of an air-pump during 

 the experiment ; when the desired temperature was reached, it 

 was sealed off at a point where the neck had been narrowed to a 

 convenient size. In 1876 Habermann '" gave a complete diagram 

 of the apparatus, replacing the air-pump by a Bunsen-pump ; 

 but although he made no alteration in the method, still it was 

 referred to by Sommaruga *' as Habermann's. 



The readiest method of determining the residual air is that of 

 Greville Williams, i^ viz., to measure by means of a burette the 

 quantity of mercury which is required to displace it. Deville 

 and Troost'^ recommended weighing the mercury required. 



Various experiments had been performed on vapours mixed 

 with air. but the main point in Playfair and Wanklyn's '* method 

 (1861) consisted in stopping the supply of vapour before the 

 bath in which the bulb was being heated had attained its 

 maximum temperature. 



Natanson,'* in 1855, in order to use the Gay-Lussac method 

 up to a temperature of 300°, heated the upper part of the tube 

 by means of charcoal in a cylindrical furnace, and determined 

 the temperature by thermometers suspended in the air-space 

 between the graduated tube and the inner tube of the heating 

 apparatus. In correcting for the tension of mercury-vapour he 

 used Avogadro's tables. 



Greville Williams'" in 1857, wishing to make some determina- 

 tions at varying pressures, devised the following method : — The 

 graduated tube is, after it has been filled and the bulb has been 

 inserted, screwed by means of a nipple cemented to the bottom 

 into an orifice in the top of a small metallic cistern into a second 

 orifice in which a long open glass tube is fitted. Into this tube 

 mercury is poured until the required pressure is obtained. To 



^ Ann. Chim. Phys. [3], 63, 53. ^ Wien. Sitz. Bcr. 53 [2], 92. 



3 Liebig'sAnn., 141, 273(1867): Phii. Ma£., 34, i (1867). 



< Ann. Chim. Phys., 68, 428. 



5 Ibid. [3], 58, 257; "Watts' Diet. Chem.," s, 373! Cmnpt. Rend., 45, 

 821 ; 49, 239. 



o Proc. Koy. Soc, 21, 203(1873). 7 "Watts Diet. Chem.," 5, 374. 



8 Deut. Chem. Ges. Ber., 11, 1196 (1878) ; Journ. Chem. Soc., December, 

 1878, p. 937. 9 "Cours de Chim.," 4, 71. 



^^ Liebig's Ann., 187, 341 (1877) ; Jaitm. Chem. Soc, 1877, voi. ii., 697. 



^^ Deut. Client. Ges Ber., 11, 1355 ; /t7«r«. CA^w. .S"(7C., January, 1879, 

 p. 63. " Phil. Trans., 1857, 460. '3 Compt. Rend., 56, 891. 



^•* Trans. Roy. Soc. Edin., 22 [3], 441 (1861); Ann. Chem. Phnrm., 121, 

 : 01(1862) ; 122, 247 (1862). "5 Jild,, 98, 301 (1856). 



" "Williams' Chem. Manip.," 542(1857). 



reduce the pressure the excess of mercury is allowed to escape bv 

 a tap in the side of the cistern. The whole is heated in a water- 

 or oil-bath. 



In Regnault's ' apparatus for the same purpose the two tubes 

 are fastened to the bottom of the water-bath, and are connected 

 by a T-piece, which is closed by a 3-way cock of special 

 construction. 



For determinations^ up to 150° Greville William.s's compact 

 modification consists in replacing the large vessel of mercury and 

 the open glass cylinder by a cylinder closed and rounded at the 

 lower extremity so as to resemble a large test-tube. This is then 

 filled to a depth of 50-60 mm. with mercury, and above that with, 

 water or oil to a convenient height. The graduated tube is filled 

 and the bulb inserted over the mercurial trough ; it is then im- 

 mer.-ied in the large tube by means of a rod having at the end a 

 small cup containing mercury. The large tube may be supported 

 on wire gauze and heated by a Bunsen burner, or may be placed 

 in a shallow oil-bath. 



Schifiin,^ in 1862, proposed steadying and manipulating the 

 graduated tube by means of a loaded handle, which was secured 

 to its upper extremity by spring clips. 



Grabowski,* in 1866, replaced the charcoal furnace of 

 Natanson by a very much neater air-bath heated by gas, but the 

 chief merit in his method is that a tube containing air is heated 

 by the side of that containing the substance. As soon as the 

 substance is all converted into vapour, air is passed up into the 

 second tube until it occupies as nearly as possible the same 

 volume as the vapour. After the operation the air is measured 

 at atmospheric pressure and temperature. 



CrouUebois,' in 1874, reverted to Eineau's method of using a 

 large globe with a long tube, but took the precaution to heat thi 

 upper portion in a water bath. Deville," however, criticised 

 his method rather severely, and pointed out that it was an 

 unwieldy apparatus to manipulate. 



In 1868, Hofmann,' in modifying the Gay-Lu?sac method, 

 while he adopted the long tube which had been previously usefi 

 by Bineau, Playfair, and Wanklyn, and Grabowski, introduced 

 such an important alteration into the apparatus that it is not 

 spoken of as his modification, but as his method. Instead of 

 heating the substance-tube by a water-, oil-, or air-bath, he 

 simply inclosed it in a slightly larger mantle tube, and passed 

 the vapour of a liquid of definite boiling-point through the inter- 

 vening space, selecting the liquid according to the temperature 

 required. By this means he not only rendered the apparatus 

 much more compact, but he maintained a steady temperature 

 with the greatest ease. Wichelhaus,' in 1870, anxious to avoid 

 the uncertainty introduced by the doubt as to the temperature of 

 the column of mercury between the bottom of the outer tube, 

 and the trough, dispensed with the latter by fixing to the lower 

 extremity of the substance-tube an inverted syphon containing- 

 mercury. Then by lengthening and suitably enlarging the lower 

 extremity of the outer tube, the whole of the inner one can be 

 surrounded by vapour. 



Grabowski," in 1875, in order to obtain a high temperature, 

 employed the vapour of naphthalene as the heating medium in 

 using Hofmann's apparatus ; but Engler,'" in the following year, 

 finding that the stoppage of the tubes from the solidification of 

 the condensed hydrocarbon was troublesome, proposed to obviate 

 the difficulty in the following manner : — He fixed to the lower 

 end of the outer tube a metal socket provided with a short side- 

 tube similar to those used for heating funnels. Then, by boiling^ 

 the heating medium in this tube and allowing the vapour to 

 cohobate in the space between the two glass tubes, he dispensed 

 with all the arrangement of flask, tubes, and condenser. 



Hofmann," at the same time, made several modifications in 

 his apparatus : I. He proposed heating the whole length of the 

 inner tube by making the outer one long enough to enter the- 

 mercury in the trough, and provided for the escape of the con- 

 densed liquid and excess of steam by having a small side-tube 

 affixed a short distance above the level of the mercury. 2. 

 Finding that graduated tubes were very liable to crack, he pro - 



' Ann. Chim. Phys. [3], 63, S' (1861). 

 = " Watts' Diet. Chem.," 5, 367. 



3 Fresenius* Zcit. Anal. Chem.. i. 321 (1862). 



4 IVien. Sitz. Ber., 53 [2], 92 (1866). 



s Compt. Rend., 78, 496 (1874) ; Journ. Chem. Soc, 12, N.S., 648 (1874).. 

 6 Compt. Rend., 78. 534, 7 Deut. Chem. Ges. Ber., i, 198 (1868). 



8 Ibid., 3. 166 (1870) ; Journ. Chem. Soc, 1870, 324 ,- 1877, vol. i. 33- 



5 Deut. Chem. Ges. Ber., 8, 1437 (1875). 



'° Ibid., 9, 1419 (1876) ■ Journ. Client. Soc, 1877, vol. i., 269. 

 " Deut. Chem. Ges. Ber., 9, 1304 (1876) ; Journ. Cliem. Soc, 1877... 

 vol, i., 33, 



