8 5 o 



NA TURE 



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I > I M1IER 2 ' 



1922 



to be a definite relation between the constitution of 

 tin- dye and its desensitising properties. The con- 

 ditions are thus very similar to those which hold in 

 the case of sensitisers. 



The great drawback to the use of Phenosafranine is 

 its pronounced staining properties ; it can only be 

 removed from the gelatin film by prolonged washing. 

 Konig has recently put on the market a desensitiser, 

 Pinaki yptol. which is claimed to be as active as Pheno- 

 safranine, but which neither stains gelatin, celluloid, 

 nor the skin, although it gives a deep green solution. 



A satisfactory explanation of the desensitising action 



of these substances is still wanting. Luppo-Cramer 

 claims that the phenomenon is connected with the 

 formation of an oxidation product of the dye. Lumiere 

 and Seyewetz have shown, however, that if an unex- 

 posed plate is bathed in a solution of Phenosafranine it 

 recovers its original sensitivity after being washed 

 sufficiently long to remove the colouring matter. It 

 is probable, according to Lumiere and Seyewetz, that 

 any oxidation product of the dye would be adsorbed 

 by the silver bromide and not be removed by washing, 

 so that the recovery in sensitivity would not be ex- 

 plicable on Liippo-Cramer's theory. 



Obituary. 



Prof. Georges Lemoine. 



M GEORGES LEMOINE. professor of chemistry 

 at the Polytechnic School, Paris, whose death 

 at tin' age of eighty-one has just been announced, was 

 born at Tonnere in 1S41. He entered the Polytechnic 

 School in 1858, and two years later became Eleve 

 inginieur at the Ecole des Ponts-et-Chaussees. He 

 early devoted himself to the study of chemistry, ami 

 investigated the compounds of sulphur and phosphorus, 

 one of which, the sesquisulphide of phosphorus, is now 

 largely employed in the igniting composition of the 

 lucifer match in place of ordinary phosphorus. The 

 substitution of this compound for phosphorus — now 

 compulsory in most countries where matches are made 

 — has been attended with the most beneficial results in 

 the industry, the " phossy jaw" of the match-worker, 

 or necrosis of the facial hones, being practically a 

 thing of the past. 



Lemoine also studied the reciprocal transformation 

 of the two best-known allotropes of phosphorus. By 

 heating known weights of phosphorus in closed flasks at 

 440 "', the temperature of boiling sulphur, for varying 

 lengths of time, and separating the products by carbon 

 disulphide.he was able to determine the influence of time 

 and pressure on the direction and extent of the change. 

 He showed that the extent of the transformation is 

 determined by the tension of the vapour, as in the case 

 of other phenomena of volatilisation and dissociation. 

 /// vacuo, the conversion of ordinary into red phos- 

 phorus becomes more and more rapid as the tempera 

 ture is raised. The rapidity of the transformation 

 varies with the amount of phosphorus used. At any 

 given moment the rapidity depends not only upon the 

 quantity of ordinary phosphorus remaining, but also 

 upon the quantity of red phosphorus already formed. 

 The phenomenon is pre-eminently one of vapour tension 

 and depends upon the capacity of the vessel in which 

 the transformation — which is never complete — is 

 'Hi Mid. These facts are now well known and are 

 uniformly acted upon in the phosphorus industry. 



Questions of chemical dynamics had alwa)'s a certain 

 measure of attraction for Lemoine, and although he was 

 not a particularly prolific contributor to chemical 

 literature, much of his published work is concerned 

 with their investigation. One of the most important 

 of these inquiries relates to the conditions of chemical 

 equilibrium of hydriodic acid. This substance was 

 chosen as suitable for the study of the general pheno- 

 mena ol chemical equilibrium for the reason that the 



NO. 2773, VOL. IIO] 



1 onstituent elements are monatomic ; they combine, or 

 dissociate, without change of volume (at the tempera- 

 ture of the experiment), and the thermal effects of com- 

 bination are very slight. The aim of the investigation 

 was to show that under given conditions of temperature 

 and pressure, a mixture of the two constituent gases in 

 given proportions will attain sooner or later a definite 

 state of chemical equilibrium in which only a certain 

 proportion of the hydriodic acid possible is actually 

 formed, varying with the temperature, pressure, and 

 proportions of the gases present, but always the same 

 for the same conditions. The conditions studied were 

 heat, pressure, mass, the action of porous bodies, of 

 oxygen and of light. The main results have long since 

 been incorporated into the general theory of chemical 

 change, and call for no detailed account. At the time 

 of their publication they constituted a notable and 

 novel contribution to chemical dynamics. 



It has long been known that mixed solutions of ferric 

 chloride and oxalic acid are decomposed by light with 

 tlie evolution of carbonic acid (Man hand, Jodin), and 

 that the rate of decomposition depends on the intensity 

 o) the light. Lemoine studied this change with a view 

 of determining how far it may be made the basis ol an 

 actinometric method. He found that for a given 

 intensity, the evolution of gas is at first uniform, but 

 that when about half the total quantity of carbon 

 dioxide has been evolved, the rate of decomposition 

 gradually diminishes. The greater the volume of the 

 liquid, the longer is the time before decomposition 

 slackens. When the two solutions are separately 

 exposed to light for several hours and then mixed, 

 decomposition takes place more rapidly than if the 

 solutions had not been previously insolated. Dilution 

 with water increases the change, due probably to hydro- 

 lysis of the ferric chloride. At ordinary temperatures 

 the mixed solutions are practically unaffected in the 

 dark. On heating, gas begins to be evolved at 50° 

 and increases rapidly in amount as the temperature 

 ri.->es. The general course of the change is. however, 

 very similar to the influence exercised by light and is 

 affected apparently by the same conditions. 



Lemoine occasionally worked at subjects of organic 

 chemistry, such as the nature of the paraffin hydro- 

 carbons and the dissociation of haloid compounds of 

 defines under the influence of heat and pressure, but 

 organic chemistry had evidently few attractions for him, 

 and his work in this special field was very limited and 

 calls for no special comment. 



