156 



NA TURE 



{June 25, 1874 



The iron tube is 4 ft. in length, and is pro\ided with a 

 central enlargement, suggested to me by Mr. Dewar, form- 

 ing a T-piece by the screwing in of a side tube, the end of 

 which is left projecting from the door in the roof of the 

 furnace. Caps are screwed on at each end of the main 

 tube ; these caps are closed by a glass plate at one end, and have 

 each a small side tube for the purpose of pasting hydro:;en or other 

 gases through the hot tube. The furnace is supplied with coke 

 or charcoal, an electric lamp connected with thiily Grove's cells 

 is placed at one end of the lube and a one-prism spectroscope 

 at the other. The temperatures reached by this furnace may be 

 conveniently divided into four stages : — 



I. When the continuous spectrum of the tube extends to the 

 sodium line D, this line not being visible. 



II. When the continuous spectrum extends a little beyond D, 

 this line being visible as a bright line. 



III. When the spectrum extends into the green, D being very 

 bright. 



IV. When the spectrum extends beyond the green and D be- 

 comes invisible as a line, and the sides of the furnace are at a 

 red heat. 



1 may add (i) that I have only within the last few days been 

 able to employ the third and fourth stages of heat, as the furnace 

 was previously without a chimney, and the necessary draught 

 could not be obtained ; and (2) that I was informed a little time 

 ago by Prof Roscoe that with a white-hot tube he had observed 

 new spectra in tlie case of Na and K. These spectra which I 

 now constantly see, when these temperatures are reached, I shall 

 call the " new spectra." 



9. The results of the experiments, so far as the visible spec- 

 trum is concerned, between the stages indicated, may be state-" 

 as follows : — 



H No absorption. 

 N 



K I have observed either separately or together, 

 (a) The line absorption line near U. 

 O) Continuous absorption throughout the whole 



spectrum. 

 (7) Continuous absorption in red and blue at the 

 same time, the light being transmitted in the 

 centre of the spectrum (as by gold-leaf). 

 (5) Continuous absorption clinging on one side or 

 other of the line. (Tliis phenomenon which, 

 so far as I know, is quite new, will be described 

 in another note. ) 

 (e) The new spectrum. 

 Na I have observed either separately or together, 

 (a) D absorbed. 

 O) Continuous absorption throughout the whole 



spectrum. 

 {7) Continuous absorption clinging on one side or 



the other of D. 

 (5) The new spectrum. 

 Zn Continuous absorption in the blue. (An imknown line 

 sometimes appears in the green, but certainly 1:0 line 

 ofZn.) 

 Cd Continuous absorption in the blue. 

 Sb New spectrum with channelled spaces and absorption in 



the blue. 

 P The same. (This, however, in consequence of the 

 extreme delicacy of the spectrum requires confirma- 

 tion. ) 

 S Channelled-space spectrum (previously observed by 



Salet). 

 As Probable channelled-space spectrum. (Observations to 



be repeated. ) 

 Bi No absorption. 



I Channelled spectrum in the green and intense bank of 

 general absorption in the violet, where at the ordinary 

 temperature the vapour transmits light. 

 Hg No absorption. 

 10. These results may be tabulated as follows : — 

 Modern 



iveiKht. 



No visible absorp'.ion. 



Line absorption. 



Probable channelled-space absorption. 

 Continuous absorption in the blue. 

 ( Channelled-space absorption -|- b.and 

 j of absorption in violet. 



200 No absorption. 



14 >, ,. 



16 Not observed. 



31 Channelled-space spectrum probable. 

 23 Line absorption. 

 65 Continuous absorption in the violet. 



l Channelled-space spectrum and absorp- 

 j in the blue. 



32 Channelled-space spectrum. 

 20S No absorption. 



II. It will be seen from the foregoing statement that if 

 similar spectra be taken as indicating similar molecular con- 

 ditions, then the vapours, the densities of which have been 

 determined, have not been in the same molecular condition 

 among themselves. Thus the vapours of K, S, and Cd at 

 the fourth stage of heat gave us line, channelled space, and con- 

 tinuous absorption in the blue, respectively. This is also evidence 

 that each vapour is non-homogeneous for a considerable interval 

 of time, the interval being increased as the temperature is re- 

 duced, 



On the alleged Expansion in ^'olume of various substances 

 in passing by Refrigeration from the state of Liquid Fusion to 

 that of Solidification, by Robert Mallet, F.R.S. 



Since the time of Reaumur it has been stated with very various 

 degrees of evidence, that certain metals expand in volume at or 

 near their points of consolidation from fusion. Bismuth, cast- 

 iron, antimony, silver, copper, and gold are amongst the num- 

 ber, and to these have recently beenjadded certain iron-furnace 

 sl-'gi. Considerable 'physical interest attaches to this subject 

 Irom the analogy of the alleged facts to the well-known one that 

 water expands between 30° K. and 32', at which it becomes ice ; 

 and a more extended interest has been given to it quite recently 

 by Messrs. Nasmyth and Carpenter having made the supposed 

 facts, more especially those relative to cast-iron and to slags, the 

 foundation of their peculiar theory of lunar volcanic action as 

 developed in their work " The RIoon as a Planet, as a W'orld, 

 and a Satellite" (4to, London, 1874). There is considtrabk 

 ground for believing that bismuth does expand in volume at 01 

 near consolidation ; but with respect to all the other substances 

 supposed to do likewise, it is the object of this paper to show 

 that the evidence is insufficient, and that with respect to cast- 

 iron and to the bassic silicates constituting iron slags, the alle- 

 gation of their expansion in volume, and therefore their 

 greater density when molten than when solid, is wholly erro- 

 neous. The determination of the specific gravity in the liquid 

 state of a body having so high a fusing temperature as cast-iron 

 is attended with many difficulties. By an indirect method, how- 

 ever, and operating upon a sufficiently large scale, the author 

 has been enabled to make the determination with considerable 

 accuracy. A conical vessel of wrought iron of about 2 ft. in 

 depth and I '5 ft. diameter of base, and with an open neck of 

 6 in. in diameter, being formed, was weighed accurately empty, 

 and also when filled w ith water level to the brim ; the weight ot 

 its contents in water, reduced to the specific gravity of distilled 

 water at 60° I", was thus obtained. The vessel, being dried, was 

 now filled to the biim with molten grey cast-iron, additions of 

 molten metal being made to maintain the vessel full until it had 

 attained its maximum temperature (yellow heat in daylight) and 

 maximum capacity. The vessel and its contents of cast-iron 

 when cold were weighed again, and thus the weight of the cast- 

 iron obtained. The capacity of the vessel when at a max- 

 imum was calculated by applying to its dimensions at 60° the 

 coethcient of linear dilatation, as given by Laplace and others, to 

 its range of in^creased temperature ; and the weight of distilled 

 water held by the vessel thus expanded was calculated from the 

 weight of its contents when the vessel and water were at 60° F. 

 after applyu'gsome small corrections. 



W'e have now the elements necessary for determining the 

 specific gravity of the cast-iron which filled the vessel wlien in 

 the molten state, having the absolute weiglits of equal volumes 

 of distilled water at 60" and of molten iron. Tf e mean specific 

 gravity of the cast-iron which filled the vessel was then deter- 

 mined by the usual methods. The final result is that, whereas 

 the specific gravity of the cast-iion when cold was 7 '170 it was 

 only 6'650 when in the molten condition ; cast-iron, therefore, is 

 less dense in the molten than in the solid state. Nor does it 

 expand in volume at the instant of consolidation, as was conclu- 

 sively proved by anotlier experiment. Two similar lo-inch 

 spherical shells i'5 in. in thickness, were heated to nearly the 

 same high temperature in an oven, one being permitted^ to cool 



