ON APPARATUS FOR VITRIPACTION. 83 



ing the progress of the experiment, have combined to hinder chemists from 

 multiplying observations on fusion, or examining with accuracy the phseno- 

 mena of vitrifaction. 



On considering what might be the best means of obtaining a great range 

 of heat for such purposes not subject to the disadvantages above mentioned, 

 and of ready application and oeconomical use, it occurred to me that hydro- 

 gen gas, self-condensed in a vessel sufficiently strong, and allowed to issue 

 with greater or less rapidity through very fine apertures, would furnish a fuel 

 and furnace to answer these requirements. 



In 1836 I expended the sum granted by the Association in executing the 

 apparatus which I had thus conceived ; and the instrument which I have now 

 the honour of exhibiting to the Section, and of which I propose to show the 

 working, is constructed on the same principles, but somewhat reduced in size 

 and altered in arrangement, so as to render it more compact and portable. 



These instruments were made at Bermondsey at the engine-factory of 

 Messrs. Bryan Donkin, to whom I am indebted for many valuable sugges- 

 tions, and whose name is a sufficient, warrant for the excellence of the work- 

 manship, and for the care with which the sti-ength of every part of the appa- 

 ratus has been ascertained. Strength is indispensable, since the principle on 

 which in this instrument I depend for obtaining perfect combustion and a 

 rapid accumulation of heat is the velocity of the jets, issuing under a high 

 degree of compression. When I stated to the late Dr. Dalton, in 1835, the 

 pressure at which I proposed to work, he expressed a doubt whether the cold 

 which would be produced by the great expansion of the gas might not be 

 found materially to detract from the heat ; and it does happen, either from 

 this cause, or as Dr. Faraday suggests, from the effect of successive explo- 

 sions, that if a strong pressure is put on at first, the jets refuse to inflame, or 

 blow themselves out ; but when the object on which they are directed is once 

 heated to a certain point, the intensity of the heat rises in proportion to the 

 velocity of the jets. The first instrument was tested by the hydraulic press 

 to a pressure of 160 atmospheres, and I have worked it when showing 80 in 

 the gauge : that which is now before the Section has been tested to 60 atmo- 

 spheres, and in the experiments which I shall show will not be subject to 

 more than from 25 to 30. I need scarcely add that under such circumstances, 

 the maximum condensation of the gas being determined by the quantity of 

 materials used for its production, and the gas itself being hydrogen almost 

 unmixed and consequently wholly inexplosive, these experiments are free 

 from all suspicion of danger. The tightness of every part of the apparatus 

 may be safely tried by a lighted taper, and if through any accidental leakage 

 the gas takes fire, it is easily extinguished by shutting the stop-cock or screw- 

 ing up the loose joint. 



The vessel in which the gas is generated and accumulated is a tube (see 

 Plate XXIV.) of drawn iron, closed at the lower end by welding and lined with 

 an internal tube of lead, of convenient height for manipulation, and hung by 

 the middle on a swivel, so as to be readily reversed and emptied of its con- 

 tents. On the upper end of the tube-turned conical a flanged iron cap is 

 driven and screwed, and on the cap a strong brass plate is screwed and ren- 

 dered air-tight by a leaden washer between it and the iron cap, which leaden 

 washer is soldered to the top of the internal tube of lead, and thus prevents 

 the acid penetrating between the iron tube and lead lining. In the brass 

 plate is a central aperture, in the form of a deep hollow cone, inverted and 

 truncated, which receives a hollow conical stopper, also of brass, ground to 

 fit it, and furnished with a stop-cock and tubular head, connected by means 

 of an union-joint with the rest of the apparatus. Two wedge-shaped ears 

 stand out from the stopper above the conical part, and wlien the joint is to be 



g2 



