62C 



NATURE 



[Oct. 26, 1SS2 



menters, and for the accuracy, so far as was required for 

 the purpose in hand, of his own experiments. His deter- 

 mination of the specific heat of air, pressure constant, and 

 the specific heat of air, volume constant, furnished the data 

 necessary for making Laplace's theoretical velocity agree 

 with the velocity of sound experimentally determined. On 

 the other hand, he was able to account for most puzzling 

 discrepancies which appeared in attempted direct deter- 

 minations of the differences between the two specific heats 

 by careful experimenters. He pointed out that in experi- 

 ments in which air wa; allowed to rush violently or explode 

 into a vacuum, there was a source of loss of energy that 

 no one had taken account of, namely, in the sound pro- 

 duced by the explosion. Hence in the most careful 

 experiments where the vacuum was made as perfect as 

 possible, and the explosion correspondingly the more 

 violent, the results were actually the worst. With his 

 explanations the theory of the subject was rendered 

 quite complete. 



Space fails, or I should mention in detail Mr. 

 Joule's experiments on magnetism and electro-magnets, 

 referred to at the commencement of this sketch. He dis- 

 covered the now celebrated change of dimensions produced 

 by the magnetisation of soft iron by the current. The 

 peculiar noise which accompanies the magnetisation of an 

 iron bar by the current, sometimes called the "magnetic 

 tick," was thus explained. 



Mr. Joule's improvements in galvanometers have al- 

 ready been incidentally mentioned, and the construction 

 by him of accurate thermometers has been referred to. 

 It should never be forgotten that he first used small 

 enough needles in tangent galvanometers to practically 

 annul error from want of uniformity of the magnetic field. 

 Of other improvements and additions to philosophical 

 instruments may be mentioned a thermometer, unaffected 

 by radiation, for measuring the temperature of the atmo- 

 sphere, an improved barometer, a mercurial vacuum 

 pump, one of the very first of the species which is now 

 doing such valuable work not only in scientific labora- 

 tories, but in the manufacture of incandescent electric 

 lamps, and an apparatus for determining the earth's hori- 

 zontal magnetic force in absolute measure. 



Here this imperfect sketch must close. My limits are 

 already passed. Mr. Joule has never been in any sense 

 a public man ; and, of those who know his name as that 

 of the discoverer who has given the experimental basis 

 for the grandest generalisation in the whole of physical 

 science, very few have ever seen his face. Of his private 

 character this is scarcely the place to speak. Mr. Joule is 

 still amongst us. May he long be spared to work for 

 that cause to which he has given his life with heart-whole 

 devotion that has never been excelled. 



In June, 1878, he received a letter from the Earl of 

 Beaconsficld announcing to him that Her Majesty the 

 Queen had been pleased to grant him a pension of 200/. 

 per annum. This recognition of his labours by his 

 country was a subject of much gratification to Mr. Joule. 



Mr. Joule received the Gold Royal Medal of the Royal 

 Society in 1852. the Copley Gold Medal of the Royal 

 Society in 1870, and the Albert Medal of the Society of 

 Arts from the hands of the Prince of Wales in 1880. 



J. T. BOTTOMLEY 



COAL-TAR 



A Treatise on the Distillation of Coal-Tar and Am- 

 moniacal Liquor, and the Separation from them oj 

 Valuable Products. By George Lunge, T'h. D., F.C.S., 

 Professor of Technical Chemistry in the Federal Poly- 

 technic School, Zurich. (London : Van Voorst, 1882.) 

 A couple of centuries have just elapsed since the first 

 English patent was granted to Becker and Serle for 

 " a new way of makeing pitch and tarre out of pit coale, 

 never before found out or used by any other" ; and in 

 1742 a second patent was obtained by M. and T. Betton 

 for the manufacture of " an oyle extracted from a flinty 

 rock for the cure of rheumatick, and scorbutick, and 

 other cases.'' Whether wc have here a foreshadowing 

 of the antiseptic method of treatment is impossible to 

 say, but that there was virtue of another sort in coal-tar 

 was fully recognised by the Earl of Dundonald, the 

 father of brave Lord Cochrane, who, towards the close of 

 the last century, set up tar ovens on a pretty extensive 

 scale in Ayrshire. 



What we know as the coal-tar manufacture is however 

 practically an industry of the present generation : it is 

 not even contemporaneous with that of the making of 

 coal-gas, for during the earlier yens of that manufacture 

 the tar was counted as the most noxious of bye products 

 to be got rid of by being buint under the retorts or bv 

 being turned into the nearest stream. We have changed 

 all that however, and to-day the tar is among those sub- 

 stances which, as Dr. Siemens pointed out the other day 

 at Southampton, make the products of the destructive 

 distillation of coal so much more valuable than the coa 

 itself. 



England is the great tar-producing country of thef 

 world ; at the present time about half a million tons o 

 tar are produced annually throughout Europe, of which 

 we make about three-fifths. The distillation of coal-tar 

 as a starting-point in the manufacture of colouring matters 

 has indeed become one of our most important chemical 

 industries. We however do not ma^e these colouring 

 matters although we are the principal users of them. 

 Although Faraday first discovered benzene, and Mansfield 

 gave his life in shoeing us how to isolate that substance 

 on the large scale, and although Perkin led the way by 

 the discovery of aniline purple, the first coal-tar colour ; 

 nevertheless the manufacture of the so-called coal-tar dyes 

 has mainly centred itself in Germany, We send to the 

 Germans the crude material, and they return to us the 

 finished products. At the same time wc also supply 

 many of the chemicals necessary to transmute the baser 

 substances into the costly dyes. In met in this matter 

 we are as mere hewers of wood and drawers of water ; a 

 circumstance which doubtless has not escaped the atten- 

 tion of the Royal Commissioners who are to report on 

 the technical education of this country. We have not 

 far to seek in tracing the cause of this : it is simply owing 

 to the extraordinary development of chemical research in 

 Germany arising largely from ihe attitude of the German 

 universities towards scientific inquiry. 



We have to thank Prof. Lunge fur what is in reality 

 the only monograph on this subject oi tar distilling either 

 in our own or in any continental language. Probably no 

 one more fitted, both from practical experience and scien- 



