ILLUMINATION. 



515 



higher, and applying a fresh lighted taper or 

 match, the temperature is found at which 

 the vapor of the oil will take fire and burn 

 steadily, or at which, as is commonly said, the 

 oil burns. As to the explosive point, however, 

 this apparatus would appear in a degree liable 

 to the objections to be made against the open 

 saucer ; as by an unnoticed current of air the 

 vapor could be for a time carried off, and 

 some dealers have stated so that the oil can 

 thus be made to show an apparent explosive 

 point twenty degrees higher than the real one 

 a great injustice, of course, to the purchaser. 

 The accompanying drawings (figs. 1 and 2) 

 represent a " Coal Oil Pyrometer " for the uses 

 just considered, arid which, though stated in 

 the " Teclmologiste" (Dec., 1862) to have been 

 invented by Messrs. H. J. Smith and W. Jones, 

 of Phila., and constructed by Mr. Giuseppe 

 Tagliabue, of New York, the latter declares to 

 be his own invention (patented, Nov., 1862). 

 The close similarity of this instrument, in many 

 of its parts, to the preceding, renders a com- 

 plete description of it unnecessary. In it, also, 

 appear the hollow cylindrical support, water- 

 bath, included reservoir for the oil, lamp, 

 and thermometer. The last named has here, 

 however, a fixed position, with its bulb with- 

 in the oil to be tested, while over the oil- 

 reservoir can be closed (as in fig. 2), or 



Fig. 1. 



Fig. 2. 



opened (as in fig. 1), a cover turning on 

 a pivot. This cover has two small orifices 

 (one marked cZ), and a larger one which opens 

 into a small cylindrical box, with a door (c) 

 in the side. The oil being introduced, the 

 cover closed, and the small orifices also closed 



by caps sliding over them, and heat being ap- 

 plied, vapor presently begins to arise from the 

 oil ; but in this condition of the instrument the 

 atmosphere does not readily enter it, and the 

 vapor tends to be confined. The application 

 of heat should be made slowly, and with the 

 precautions before named. "When the suppos- 

 ed explosive point of the vapor is nearly reach- 

 ed, upon opening the small orifices in the cover 

 the upper chamber at once becomes filled with 

 a mixture of the vapor and air, and a lighted 

 taper being introduced through the door (c), 

 if the point of free vaporizing of the oil has 

 been reached, a slight explosion or "puff" 

 within this chamber will indicate the fact. By 

 sliding off the cover, and heating, the point 

 at which the vapor takes fire on the surface 

 of the oil this being usually (as found with 

 this instrument) some 8 to 10 or more above 

 the explosive point is readily found. 



The instruments thus far named are small, 

 not expensive, and easy of use. It is declared 

 by some that, even with that last named, an 

 oil can be made to show too high an explosive 

 point ; but it is doubtless true that, with either 

 of them, by a proper understanding and care, 

 and repeating, if needs be, a fair and useful 

 test of the explosive point of oils liable to con- 

 tain naphtha can be obtained. Prof. John 

 Torrey, of New York, declares Mr. O. Taglia- 

 bue's instrument superior (in accuracy, impli- 

 ed) to those in which the cup is open or un- 

 covered. Still it must be kept in mind that 

 these tests show the explosiveness and com- 

 parative safety of oils only, and cannot be re- 

 lied on to indicate the proportions of light and 

 of heavy oils, and so, the endurance and value 

 of an oil for lighting. 



RegnaulCs Apparatus for Fractional distil- 

 lation of Coal Oils, Petroleum, etc. M. "W. 

 Eegnault has very recently invented an appa- 

 ratus intended to serve the purpose indicated 

 at the close of the preceding section ; that, 

 namely, of determining analytically the per- 

 centage of the component oils having differ- 

 ent densities and boiling points which are 

 contained in a given coal or rock oil, or in any 

 derivative from one of these, the separation 

 being effected by means of fractional distilla- 

 tion. Essentially, the apparatus consists of 

 an upright cylindrical copper retort capacity 

 about 300 cubic centimetres with a lamp- 

 stand and lamp underneath for heating, and 

 at its upper part communicating by a tube 

 with the interior hollow brass cylinder of 

 a condensing arrangement (also upright), this 

 cylinder being enclosed within a consider- 

 ably larger one, while into the lower part of 

 the space between the two a stream of cold 

 water is, by means of a funnel and tube, con- 

 tinually allowed to flow; the heated water, 

 meanwhile, escaping through another tube at 

 its top. The condenser is prolonged into a 

 small tube at top, and also at bottom ; and the 

 whole being supported by an iron tripod, a 

 row of glass cylinders, say five in number, 



