March 29, 19 17] 



NATURE 



85 



could obtain a continuous current in a closed circuit. 

 These are two cases of perpetual motion. The prin- 

 ciple of conservation of energy which is here appa- 

 rently violated is inapplicable to such cases where the 

 forces are so much smaller than any experimental 

 results on which that principle rests. 



The temperature effect of gravitation is a residual 

 effect of gravitation which is itself apparently a re- 

 sidual effect, so thgj: we are dealing with forces of, 

 say, 10-'- dyne. 



The fact that the forces involved in the above sug- 

 i^ested cases (a) and (b) are far too small to render any 

 jjerpetual effects observable, of course does not affect 

 the argument, which is that the speculation does 

 involve a theoretical continuous motion. 



P. E. Shaw. 



University College, Nottingham. 



Talbot's Observations on Fused Nitre. 



Some years ago in studying the position of the 

 solidus curve in the binary system consisting of the 

 nitrates of potassium and sodium, the present writer 

 became well acquainted with the phenomena referred 

 to bv Lord Rayleigh in his interesting letter in Nature 

 of February i. A number of photomicrographs 

 were made of thin layers of the nitrates, crystallised 

 from fusion, between crossed Nicols, and it was 

 found very- necessar}' in the work that the exposures 

 should be made before the secondary change, the 

 arrival of which, as Talbot observed, is hastened by 

 scratching, had set in. There is, of course, now no 

 mystery as to the cause of this secondary change upon 

 cooling in the character of the crystals first formed 

 from the melt, for potassium nitrate is known to be 

 dimorphous, with a transition temperature at ordinary- 

 pressure about 129° C. A considerable degree of 

 under-cooling often occurs, and the transition, initiated 

 at Talbot's needle-point, spreads "like a wave " if the 

 slide be cooler than 129°, as Lord Rayleigh found 

 using a temperature near 100°. 



If Wallerant is correct in supposing that there is 

 a third, in all circumstances metastable, crystalline 

 variety of potassium nitrate, still further entertain- 

 ment from this interesting, if old-fashioned, salt is 

 at least possible. ' Alan W. C. Menzies. 



Princeton L'niversity, Princeton, N.J. 

 February 24 



POSITION AND PROSPECTS OF PROFES- 

 SIONAL CHEMISTS. 

 IX August, 1914, chemists, in common with 

 other professional men, volunteered in con- 

 siderable numbers for active service with the fight- 

 ing- forces. Many were already attached to the 

 Officers Training Corps of their universities, or 

 to Territorial units — the call was the same to them 

 as to others. The need for fit men was the first 

 consideration, and the need for chemists, as such, 

 in other spheres directly connected with war was 

 not at first recognised. Offers to the War Office 

 of scientific assistance emanating from organised 

 bodies and from individuals were politely acknow- 

 ledged and pigeon-holed for future reference in 

 case of necessity. 



We possessed, fortunately, a number of 

 chemists acquainted with the production of explo- 

 sives, but as the magnitude of the task before us 

 became better realised a much greater demand 

 arose for chemists to control the operations of 

 manufacture. 



NO. 2474, VOL. 99] 



In the early months of the war lists of chemists 

 available for the service of the country were pre- 

 pared by the Institute of Chemistry, the Chemical 

 Society, and other bodies interested in chemical 

 science, with the result that when the Ministry of 

 Munitions called for them a ready response was 

 forthcoming from all parts of the country, from 

 industrial concerns and private laboratories as 

 well as from the universities and colleges, both at 

 home and in the Overseas Dominions. The 

 majority of chemists with experience in the explo- 

 sives industry were already engaged on war work, 

 and arrangements w-ere made for the training of 

 others to take charge of operations in new- 

 factories erected in various parts of the kingdom. 

 Additional chemists were also needed for the 

 increasing work of the staffs of Government 

 laboratories and factories and to control 

 and assist in the production of war material 

 of all kinds. For certain requirements essen- 

 tial to the production of armaments and 

 munitions, for a number of drugs, for labora- 

 tory glass and porcelain ware, filter-paper and 

 other necessaries, we had hitherto been almost 

 entirely dependent on Germany and Austria, and 

 this state of affairs would have led to serious 

 difficulties if our chemists had not speedily and 

 successfully dealt with such matters. Students 

 in college laboratories assisted, under the super- 

 vision of their professors, in the preparation of 

 drugs and the examination of materials, or left 

 before finishing their courses to take up positions 

 in works. \\'omen science graduates, mostly 

 teachers in time of peace, obtained app)ointments 

 in analytical laboratories as substitutes for 

 chemists who had joined the forces or been trans- 

 ferred to war work. The demand for trained 

 analysts and works chemists still persists, and has 

 been accentuated by the undoubted fact that 

 manufacturers generally are learning to appreciate 

 more and more the value of science in industry. 



In addition to the activities referred to above, 

 mention must be made of the help rendered to 

 the Government by leading consulting chemists, 

 professors of chemistry, and technologists, in an 

 advisory capacity, with regard to inventions and 

 to offensive and defensive measures, wherein many 

 of our best are pitted against the much-vaunted 

 chemists of the enemy. German chemists had 

 obviouslv devoted attention to the employment of 

 scientific frightfulness in warfare which other 

 nations, if such means had occupied the minds of 

 their men of science at all, would have refused to 

 believe that any civilised people would adopt. 

 British chemists, therefore, were perforce called 

 upon to investigate problems wholly repugnant 

 to their inclinations and degrading to their science 

 in order to fight the enemy with his own weapons. 

 Much of what they have done must remain, and 

 probably will always remain, a sealed book ; but 

 the results are shown in the well-deserved praise 

 accorded them in the despatches of Lord French 

 and Sir Douglas Haig. 



When the Germans started using asphyxiating 

 gases, the War Office called for volunteers with 

 training in chemistry and formed with little diffi- 



