November 2, 191 1] 



NATURE 



19 



were tolerably well advanced with their methods of de- 

 silverisation. 



The Electrical Review for October 13 discusses in a lead- 

 ing article the question as to whether there is or is not at 

 the present time a demand for technical men in the elec- 

 trical engineering profession. After reviewing the evidence 

 afforded by recent letters to the Press, it concludes that 

 the overcrowding of which there have been complaints is 

 confined to the lower branches, and that it is due to the 

 large class of men who have had no technical training. 

 While the general impression that the profession was over- 

 crowded has led to a decrease in the entries of students in 

 the electrical engineering colleges, a decrease which has 

 now gone on for several years, there is to-day, as a matter 

 of fact, a greater demand for technically trained men than 

 the colleges can supply. 



In order to clear up the small diiTerences which still 

 I exist in the determinations of the melting points of metals 

 like zinc, and cadmium by even the most accurate observers, 

 I Drs. Holborn and Henning, of the Reichsanstalt, have 

 I compared together a number of platinum thermometers 

 and two constant-volume gas thermometers of Jena glass 

 59 III., and of quartz glass filled in turn with nitrogen, 

 hydrogen, and helium. Both the Jena and the quartz glass 

 were slightly porous to the helium above 200° C, but the 

 former showed no signs of being permeable to hydrogen 

 up to 450° C. The constant 5 of the platinum thermo- 

 meters lay between 1-486 and 1-510, but in no case did the 

 temperature between 200° and 450° C. determined by the 

 platinum thermometers with the use of the 5 formula differ 



I by o-i° C. from the temperature given by the gas thermo- 

 meters. The following melting and boiling points were 

 obtained: — tin, 231.8°; cadmium, 320-9°; zinc, 419-4°; 

 j naphthalene, 217-96°; benzophenone, 305-89°, on the 

 thermodynamic scale. 



Furs which are moth-proof owing to the substitution of 

 indiarubber -for animal tissues would seem at first sight 

 to be a fantastic stretch of the imagination only. A 

 curious invention recently recorded, however, would appear 

 to render rubber-backed fur a possible and practical article 

 of the near future. Large skins, or small pelts sewn 

 together, are stretched upon a frame with the fur upper- 

 most in a large flat-bottomed receptacle, which is then 

 filled with water and placed in a freezing chamber. The 

 plate of ice is then removed, and with suitable machinery 

 a thin layer is sawn from the bottom, thus removing the 

 skin, which after thawing is sold for the purposes of 

 leather. The lower surface of the remaining plate is then 

 melted until the fur is slightly exposed, when a coating 

 af rubber solution is applied layer by layer. When the 

 requisite thickness is obtained the rest of the plate con- 

 taining the fur is melted, and a large seamless pelt, with 

 i. sheet of rubber at its base, is the result. Cheapness is 

 Jne of the many advantages claimed by the inventor. 

 Ladies with valuable furs, which annually cost a consider- 

 ible sum for cold storage, will wish every success for so 

 ngenious an invention. 



Some interesting observations regarding the formation 

 )f hydrocyanic acid during the germination of seeds are 

 ;ontained in a paper by C. Ravenna and M. Zamorani 

 n the Gazzetta Chimica Italiana for September 19 (vol. 

 ill., ii., p. 74). The old experiments of Jorissen and the 

 nore recent ones of Soave have shown that some seeds, 

 iich as sweet almonds and the seeds of Mespilus japonica, 

 orm considerable quantities of hydrogen cyanide at the 

 >eginning of active life. On the other hand, the experi- 

 nents of Guignard with Phaseolus lunattis point to a 

 destruction of hydrocyanic acid at the commencement of 

 NO. 2192, VOL. 88] 



germination, especially in the case of etiolated plants. 

 The experiments now described were made on two species 

 of seed, viz. Sorghum vulgare, which does not contain 

 appreciable traces of hydrogen cyanide, and a variety of 

 linseed, which contained it in considerable proportion. In 

 the case of the former, hydrogen cyanide was elaborated 

 during germination up to a certain point, beyond which it 

 appeared to undergo progressive destruction ; in the latter 

 case a continuous increase of hydrogen cyanide was 

 observed without a point of decomposition being attained. 

 In all cases the rate of production of the cyanide was 

 greater in the green than in the etiolated plants ; but on 

 watering the latter with a 2 per cent, solution of glucose 

 during growth, the proportion of hydrogen cyanide formed 

 was increased up to the level of the green plants. The 

 amount of carbohydrates in the seed thus greatly affects 

 the formation of the hydrocyanic acid. The source of the 

 nitrogen remains to be investigated. 



The council of the Institute of Chemistry has inaugurated 

 a series of lectures, the first of which was delivered by 

 Mr. Bertram Blount at King's College on October 26. The 

 chair was taken by Prof. J. Millar Thomson, F.R.S., who 

 said the lectures were an extension of the work of the 

 institute on lines directed to benefit advanced students of 

 chemistry. Except for one or two lectures delivered in its 

 early history, the institute has not assumed in any way 

 the functions of a teaching body, though the charter 

 provides for such functions. Mr. Blount limited his re- 

 marks to calcareous cements, and more particularly to the 

 Portland cement industry. Calcareous cements, properly 

 so called, while being plastic, are capable of hardening 

 and are resistant to water. The common fallacy, that the 

 setting of lime mortar is due to the action of lime on the 

 sand with which it is mixed, was once more exploded. 

 Some siliceous materials have an advantage over others as 

 aggregates for mortar. These are known generally as 

 " pozzolanas," and their usefulness depends on the 

 hydrated silica or attackable silicates they contain, which 

 interact with lime and form compounds resistant to the 

 action of water. There seems to be no record that lime- 

 stones were intelligently chosen for the hydraulic quality 

 of the lime which they furnished until the time of Smeaton, 

 who, in considering with what material he should build 

 the Eddystone Lighthouse, ascertained that Aberthaw lime- 

 stone was undoubtedly hydraulic. Those limestones which 

 are most hydraulic contain the largest proportion of 

 argillaceous material. This quality may be improved by 

 the addition of what is capable of conferring hydraulic 

 properties on ordinary lime. Mr. Blount also discussed the 

 manufacture of so-called " Roman cement," a crude form 

 of Portland cement made by burning lumps of clayey lime- 

 stone. Starting with the notion of imitating Roman 

 cement, the progenitors of the Portland cement industry 

 arrived at the idea that when^ chalk and clay were mixed 

 and burned an hydraulic material was produced which, 

 when ground, would set and form a strong, sound cement. 



OUR ASTRONOMICAL COLUMN. 



Astronomical Occurrences for November : — 

 Nov. 6. 3h. 37m. Moon eclipsed, partly visible at Greenwich. 

 ,, I2h. iim. Saturn in conjunction with the Moon 



(Saturn 4° 18' S.). 

 7. 7h. 19m. Mercury in conjunction with Jupiter 



(Mercury 1° 50' S.). 

 ,, 2oh. 50m. Mars in conjunction with the Moon (Mars 



2°53'S.). 

 9. iSh. om. Saturn at opposition to the bun. 

 10. 2ih. 31m. Neptune in conjunction with the Moon 

 (Neptune 5" 52' S.). 



