April 27, 1893] 



NATURE 



615 



'COuld not be found qualified for original research. It was not 

 that natives of India had not in them the necessary qualifica- 

 tions ; it was that the power lay undeveloped in them , and had 

 not been brought out by a training in habits of observation. 



Messrs. Swan Sonnenschein and Co. have in the press and 

 will shortly publish a work by Dr. Edward Berdoe, entitled 

 *'The Healing Art," a popular history of the origin and growth 

 of medicine in all ages and countries. 



At a recent meeting of the Societe Fran9aise de Physique 

 M. Janet gave an account of his experiments on electric oscil- 

 lations of medium frequency (about io,ooo per sec). The 

 arrangement he employs is as follows : — A battery of accumu- 

 lators furnishes a current which passes through a high resistance 

 CD and a low resistance AB placed in series. The ends of AB 

 are joined to the plates of a condenser and also to the extrem- 

 ities of a circuit AHB. The latter consists of a coil of self-in- 

 duction L and resistance — joined in series with an equal non- 

 inductive resistance. The quantities RL and the capacity of 

 the condenser are so chosen that when the circuit is broken at 

 AB oscillations are set up in the condenser circuit. By means 

 of an interruptor, closely resembling that used by Mouton in his 

 work on the discharge of a condenser, the differences of potential 

 ■^1 and <fj at the extremities of the inductive and non-inductive 

 resistances are determined at different times after the breaking 

 of the primary circuit, and the values plotted on a curve as 

 functions of the interval after the break. If i is the current in 

 the circuit AHB at any instant then the first curve gives the 



value of — I + L^', and the second that of -? i ; so that iJ^^ 

 2 dt 2 dt 



is equal to the difference of the ordinates. The value of -^ ^. 



2 dt 

 can be obtained from the second curve, so that if the self-in- 

 duction is constant during an oscillation the ratio of these two 

 quantities will be constant. This is found to be so, the value of 

 L deduced from the curves being constant and also independent 

 of the capacity of the condenser and of the electromotive force 

 employed in the primary circuit. The author has also obtained 

 from his observations the value at each instant of the difference 

 of potential V between the plates of the condenser (a mica one) 



and of the charge Q, and he finds that the quotient ^, repre- 

 senting the capacity of the condenser, is greater for decreasing 

 than for increasing values of V. The shape of the curves ob- 

 tained recall those Ewing has found in the case of the mag- 

 netisation of iron, and indicate a kind of hysteresis or viscosity 

 in the dielectric. 



The problem of obtaining a well-defined and trustworthy 

 standard for the intensity of a source of light can hardly be said to 

 be completely solved. Violie proposed as a unit the amount of 

 light radiated by one square centimetre of molten platinum at the 

 moment of solidification. But in order to keep the platinum 

 absolutely pure, and its surface clean and smooth, it would be 

 necessary to melt large quantities of the metal in an electric fur- 

 nace. Siemens proposed platinum foil at the instant of melting^ 

 but a series of 500 meltings gave deviations of 10 per cent, in 

 spite of the greatest precautions, mainly on account of the tearing 

 of the foil on melting. According to a report recently presented 

 to the Reichstag, the physicists of the Imperial Phy?ico-Techni- 

 cal Institute at Berlin have been endeavouring to make Siemens' 

 unit available for practical purposes by fixing the temperature of 

 the platinum in some manner independent of its melting point. 

 It was found that at any given temperature the ratio of the total 

 radiation to that transmitted by a layer of water of a certain 

 , thickness was constant within 2 per cent, for plates of platinum 

 of different thicknesses and from different sources. To measure 

 NO. 1226, VOL. 47] 



the amounts of radiation a very delicate bolometer was con- 

 structed. A piece of platinum foil was welded on to a piece of 

 silver foil often times its thickness, after which the combination 

 was rolled between copper rollers down to a thickness of j J^ 

 mm. It was then cut in a dividing machine so as to form a 

 long continuous strip of i mm. breadth within a small area. Four 

 such strips were mounted in a frame, and freed from silver by 

 etching with acid, thus leaving strips ^wu ™™' thick. When 

 tested, the bolometer was found to be extremely satisfactory. 

 The Institute is at present engaged on determining the absorptive 

 action of water and of the quartz vessel containing it. Further 

 important questions are those regarding the effect of impurities 

 in the platinum and the kind and duration of incandescence, 

 questions which must be answered before the method can be 

 regarded as thoroughly practical. 



Amidophosphoric acid, P0.NH2.(0H)o, the primary amine 

 of orthophosphoric acid, has been isolated by Mr. H. N. 

 Stokes, and its properties and those of several well-crystallising 

 salts are described by him in the March number of the American 

 Chemical y ournal. It has hitherto been found impossible to 

 obtain this substance owing to the extreme difficulty of regulat- 

 ing the decomposition by water or acids of the products 

 obtained by the action of ammonia on pentachloride or oxy- 

 chloride of phosphorus. It has now been obtained, how- 

 ever, by employing, instead of the two latter compounds, 

 the ethers of phosphoric acid. The most advantageous 

 method is to dissolve the chloride of diphenyl phosphoric 

 acid, PO.CKOCgH,),, in alcohol and to react upon it with 

 alcoholic ammonia, when a beautifully crystalline substance, 

 diphenylamidophosphate, PO.NH„.(OCGHg)2, is at once 

 formed. This diphenyl ether of amidophosphoric acid yields 

 an alkaline salt of amidophosphoric acid upon saponification 

 with caustic potash or soda ; upon converting this into the lead 

 salt, decomposing the latter with sulphuretted hydrogen, and 

 precipitating with alcohol, the free acid is obtained in the form 

 of fine microscopic crystals. In the actual preparation it is not 

 necessary to first isolate the chloride of diphenylphosphoric 

 acid. It is only necessary to boil one molecular equivalent 

 of phosphorus oxychloride with two molecular equivalents of 

 phenol in a flask attached to a reflux condenser until no further 

 evolution of hydrochloric acid occurs : the product contains, 

 along with other derivatives, the chloro-diphenyl ether required. 

 The liquid only requires to be diluted with alcohol, when the 

 alcoholic ammonia may be directly added and the crystals of 

 the amido diphenyl ether precipitated. Diphenylamidophos- 

 phate is a comparatively stable substance melting at 148° and 

 resolidifying to a mass of crystals. The crystals are readily 

 converted into acid potassium or sodium amido phosphate by 

 means of a concentrated solution of caustic potash or soda ; the 

 reaction is very energetic and is complete in ten minutes. Upon 

 acidification with ice-cold acetic acid and addition of alcohol, the 

 acid salt is precipitated. Acid potassium amidophosphate, 



PO^OK , crystallises in six-rayed stars or rhombohedra ; the 



\OH 

 neutral salt is extremely soluble in water and is very difficult to 

 obtain crystallised. The acid sodium salt usually forms small 

 hexagonal crystals, and the neutral sodium salt also crystallises 

 well and, unlike the potassium salt, is not deliquescent. The 

 lead salt is obtained in the form of a precipitate, consisting of 

 groups of radiating plates, upon adding a solution of lead 

 acetate to a solution of the acid potassium salt. In order to 

 obtain the free acid from it, the crystals are suspended in iced 

 water and a current of sulphuretted hydrogen allowed to bubble 

 through. The filtrate from the sulphide of lead may then be 

 allowed to fall directly into alcohol when the crystals of amido- 

 phosphoric acid are at once deposited. 



