Feb. 13, 1879] 



NATURE 



339 



On the Combustion of Different Kinds of Fuel 



I HAVE read with interest the criticism of Mr. I, Lcwthian 

 Bell (Nature, vol. xix. p. 175) on my paper on the mode of 

 combustion in the blast furnace hearth. You say with truth 

 that the question is not simply technical, but is one of scientific 

 importance. The prevailing opinions, which Mr. Bell has ex- 

 pressed with his usual force, rest ujjon experimental determina- 

 tions of the gases in the hearth. I have never felt that trust- 

 worthy results have been obtained in any of the published 

 analyses, and with your permission I would like to state the case, 

 and see if my difficulties are removable by the wide experience 

 of Mr. Bell or other investigators. 



The blast-furnace hearth is a cylinder, closed at the bottom, 

 but perforated near the top by a number of openings in which 

 the tuyeres, or ends of the air blast-pipes are closely fitted. The 

 air enters at a pressure which usually varies in anthracite practice 

 between four and seven pounds to the square inch. As the dis- 

 charge is at the top of the furnace, many feet higher, the air 

 must describe a curved path from the point of entrance to the 

 centre of the furnace, being acted upon continuously by a hori- 

 zontal and a vertical force. It is evident that the level of the 

 tuyeres is not the place to obtain the first products of combustion 

 unless they are drawn through a tuyere in action. Elsewhere 

 the samples would not be taken from the path of the air, which 

 is upward firom the tuyere from the instant it enters the hearth. 



Mr. Bell and other investigators have analysed gases drawn 

 from the hearth by means of porcelain tubes introduced through 

 a closed tuyere aperture, or dirough holes drilled between the 

 tuyeres. It seems to me these analyses are vitiated by the mode 

 of drawing off the gas, and since this criticism applies to the 

 experimental basis of existing views of combustion in confined 

 spaces and with limited suppUes of air, I \s-ill give a few details 

 to show the scope of my objection. 



At the Wear furnace Mr. Bell drew off gas through a tuyere 

 that was closed for the piu^wse, but air was entering at other 

 tuyeres on each side and four feet distant. Certainly this did not 

 represent the product of that active combustion which takes 

 place in the path of the air, but of these products after they had 

 filtered through nearly four feet of glowing fuel What the 

 exact distance was depends upon the velocity of gas in the 

 crucible of the Wear furnace and the inner diameter of the 

 hearth, but was probably over three feet. 



The quantity drawn off is not mentioned, but as it was taken 

 for eudiometric analysis, the amount was probably le=s than five 

 litres, and the movement of the gas through this glowing coal to 

 the sample tube must have been extremely slow. Under these 

 circumstances, whatever the product of combustion in the path 

 of the air may have been, there could be only one gas drawn 

 into the sample tube, and that would be carbonic oxide mixed 

 with nitrogen. Even if we assume that the product of com- 

 bustion in the furnace is carbonic anhydride alone (which is not 

 true), this would be completely reduced to carbonic oxide by 

 passing through the hot coal. 



The experiments made on gas which was drawn through tabes 

 in holes inserted between the tuyeres do not impress me more 

 favourably. There the tubes were thrust "a little way into the 

 contents of the furnace." That description does not apply to 

 the mode in which gas samples were drawn off for analysis, but 

 to experiments for testing the reducing powers of the gas by 

 submitting pieces of ore to its action. Still it is probably 

 also the mode in which samples were obtained, and the 

 object of this note is to ascertain whether more carefiil means 

 of sampling the unchanged products of combustion were used. 

 If not, I submit that the analyses which form the basis of all 

 modem reasoning on this subject must be rejected. The rapidity 

 with which red hot carbon reduces carbonic anhydride, and 

 produc s just the gas which experimenters find in their sample 

 tubes, is well known, and methods of sampling which take no 

 precautions to guard against this change cannot be accepted. I 

 think the investigators owe it to science to give the world some 

 hint of the means they have used to prevent this action, and to 

 obtain the gas as it is formed. In the case of one of our 

 American furnaces — a small on — the blast has an upward 

 velocity of twenty feet per secoi.d at the level of the tuyeres, 

 wthout considering the increase of volume by its rise in tempe- 

 rature in the furnace, and also allowing it to penetrate instantly 

 to the centre, so as to cover the whole ara of the crucible. That 

 cannot be true, and on the other hand the withdrawal of gas 

 from the walls at the tuyere level, while the air is entering with 



great velocity four feet away, can hardly give a fair sample of 

 Sie unaltered result of immediate combustion. 



John A. Church 

 Columbu?, Ohio, U.S.A., January 21 



Internal Resistance 



The following method of measuring the internal resistance of 

 a battery was devised some two years ago by Lieut. A. R. 

 Conden, United States Navy, then attached to this station as 

 Instructor in Electricity. It fulfils quite closely the conditions 

 indicated by Clerk Maxwell on p. 412, vol. L of his treatise on 

 Electricity and Magnetism. As it is not generally known, I 

 venture to call your attention to it. 



In the figure, B is the battery, G a galvanometer, R and Rj 

 resistances, k'' a key for introducing the shunt s, and k' another 

 key for shunting out the resistance R. 



^l-IIl 



When both keys are open the current through the galvano- 

 meter is — 



E 



St = 



B -h G -h R -h R, 



When both keys are closed the current from the battery divides, 

 part going through G and R^, part through s. The current 

 tkrovgh the galvanometer is now — 



B -I- 



(G -t Ri)s G -h Ri -f s 



G -1- R, -1- S 



If Sj = Sj, then- 



B -h G 4- R -f R, 



Solving for B — 



B -J- 



(G+Ri) S G -f Ri -1- S 



G -h R, -1- S 



G -h Rj 



Finally, if B. have been adjusted equal to G -^ Rj, then — 

 B = s directly. 



In practice R is a rheostat tmplugged to eqxial G -f Rj, and the 

 two keys are combined in one. If the current be small enough 

 with G -h R then Rj may be omitted and R made equal to G. 

 s is adjusted until, upon closing the double key, the deflection of 

 the needle remains unchanged. The resistance of the battery is 

 then the resistance of the shunt. 



The case and concordance of the results obtained in this way 

 through long series of measurements are no less striking than 

 the rapidity with which the observations may be made. 



Torpedo Station, Newport, R.I., C. F. Goodrich 



January 12 



The Formation of Mountains 



Mr. G. Darwin has shown that, on the supposition that the 

 earth is a cooling solid, the depth at which the maximum cooling 

 and consequently, in aJl probability, the maximum contraction 

 takes place, moves downwards, and, taking Sir W. Thomson s 

 values of the constants, has not yet got down so far as ico miles. 



This shallowness of the layer hitherto chiefly affected is alone 

 sufficient to prove how small an effect can be attributed to such 

 a cause. 



He inquires whether I may not have under-estimated the con- 

 traction of rock in cooling. In my calciilation I put it at 

 •COOC07 linear for one degree Fahr. I derived this estimate from 



