516 ABSTRACTS OF CHEMICAL PAPERS APPARATUS, ETC. Application of Cryoscopy in Chemical Analysis. M. Drapier. (Compt. Tend., 1915, 161, 461-463.)-1t is pointed out that cryoscopic methods may often be employed for the estimation of a, component of a mixture in cases where chemical methods fail and other physical methods are not applicable on account of close similarity of constants. Case I.-A binary mixture of two bodies, A and B, such as might be isolated in fractional distillation where the boiling-points lie near together.Let A, in the pure form, serve as the cryoscopic solvent, then a solution of p grms. of the mixture in P grms. of pure solvent causes a depression in freezing-point proportional to the concentration of B in the mixture. This may be found by determining the depres- sion caused by dissolving p grms.of pure B in P grms. of A . Generally the fact that the weight P is increased by the weight of A in the mixture may be neglected ; when this is not the case, as when the mixture is poor in By the exact result must The author illustrates two hypothetical examples : be attained by successive approximations. Case II.-It may be necessary to estimate the mixture of A , B, C, etc.The depression caused by R of a solvent foreign to the mixture gives the relation where k is the cryoscopic constant of the solvent, proportion of A in a complex grms. of the mixture in P grms. x, y, x , etc., are the weights of A , B, C, etc., in R grms. of mixture, and M , H', W', etc., the respective molecular weights. Let MI = the mean molecular weight of the components B, C, etc.-that ia, the ratio of the weights of these bodies contained in R grms.of mixture to the number of their molecules ; the above equation then takes the form (1) A = ~ l o o k (-+T-x), x P J I M , The value of Nl may be calculated by making a cryoscopic determination of the mixture, using the pure substance A as the solvent. Then where k' is the cryoscopic constant of the substance A, and A' depression of freezing-point caused by dissolving T grms of the mixture in P grms.of A . Replacing the value of Nl calculated from (2) in equation (l), the expression becomes : P [ N look' 1 ' 100 k x A(P+z) A = . - . _ - -+ _____ whence M.P (UA - kA') k (MA' - look')' X=----..---- If the quantity x is negligible in comparison with P, the expression may be simpli- fied as follows : x= N.P (k'A- k A ) 100 kk' -' J.F. B.APPARATUS, ETC. 517 Reducing Power of Photographic Developers as Measured by their Single Potentials. F. C. FPary and A. N. Nietz. (J. Amer. Chem. SOL, 1915, 37, 2246-2263).-The reducing power of a developer may be expressed in terms of the concentration or partial pressure of the hydrogen produced in a platinised platinum electrode immersed in the developer until equilibrium is attained. This partial pressure may be determined from the difference between the potential (EHJ of a platinised electrode saturated with hydrogen at atmospheric pressure in contact with the developer, and the single potential (Ex) of an ordinary platinised electrode in the developer of the same composition.Then, at 25’ C., E H 2 - Ex= E = 0.05909 log. $, C where C’ is the hydrogen pressure to be measured. Several causes operate against the attainment of equilibrium in the determination of the single potential of the developer solution ; for instance, the influence of residual traces of oxygen in the system, and the slow diffusion of the hydrogen through the liquid into the electrode and into the space above the liquid.There appears also to be a sort of ‘‘ reaction-resistance,” inherent in the reducing agent itself, which in some cases (e.g., hydroquinone) delays equilibrium for several months, although in other cases (e.g., amidol) it is reached within a week. The apparatus was devised so that the developer could be dissolved in vacuo in oxygen-free water, and transferred t o the electrode cells attached to the same apparatus, which had also been evacuated and washed out both with nitrogen gas and with the developer.After filling, the cells were sealed up under vacuum and put aside for observations with the potentio- meter. Determinations of the hydrogen potential were made in a special apparatus containing the developer, through which a current of pure hydrogen gas was passed, while the electrode was suspended above the liquid and a platinum wire connection dipped below its surface ; equilibrium was attained within fifteen minutes.A large number of observations were carried out with typical developers of standard formuls. I n the case of hydroquinone, a developer of low reducing-power, equili- brium was not reached even after three months, but a mixture of hydroquinone and thiourea, which is a very powerful reducing agent, came to equilibrium rapidly at a high value, and subsequently fell to a lower value, at which it attained a second equilibrium.It is assumed that this second stage corresponded with the decompo- sition of all the thiourea present, and that the lower equilibrium represented that due to hydroquinine alone, The following values are given for reducing powers, taking hydroquinone as unity : Metol-hydroquinone, 2.7 ; amidol, 36.0 ; thiourea, 53-3 ; and reasons are given showing that these relative values are probably correct in 8 photographic sense.J. F. B. Thermostat for Moderate and High Temperatures. J.L. Haughton and E. Hanson. (Inst. of MetaZs, pp. 1-7, September, 1915.)-The apparatus first devised is shown in Fig. 1. The tube from the bulb leads, through a three-way tap, A , to the U-tube containing mercury ; another three-way tap, B, serves to connect the other limb of the U-tube with the air or with a second bulb, C, which is kept at a constant518 ABSTRA.CTS OF CHEMICAL PAPERS temperature by being immersed in a Thermos " flask filled with ice.A platinum wire, D, sealed through the wall of the U-tube and prolonged downward inside it, makes permanent contact with the mercury, whilst a similar wire, E, on the other side, at a, point where the tube is constricted, makes contact with the mercury as the latter rises in the limb, the contact being again broken as it, falls. The height of the wire, E, and the amount of mercury in the U-tube are so arranged that the pressure in the furnace bulb is slightly less than atmospheric, so that, should the bulb break, the current would be switched off.The three-way taps, though not necessary, ren- der the adjustment a matter of great ease; immersing the bulb, C, in ice neutralises IR.SPEC I PlCN. i FIG. 2. the effect of changes of room temperature. The mercury switch operates a relay which, through a resistance, cuts in or out a definite amount of the current supplied to the furnace ; the variations in current caused by the relay are just amply large enough to cover the range of accidental variations. The whole apparatus (furnaca, relay, etc.) is run off a 100-volt circuit.A more constant temperature may be obtained by constructing the furnace bulb as shown in Fig. 2. This is built into an electric furnace, the heating wire being wound on to asbestos paper wrapped directly round the bulb, and the inner tube containing the specimen is packed with asbestos in front of and behind the specimen. I t was found that a temperature of 305" C. could be maintained for two days with a variation of about 1". The furnace bulb may be constructed of glass for temperatures up to about 500' C. ; €or higher tem- peratures it should be made of silica,. I t was noticed that when a new bulb was used the temperature wag always inclined to rise for a few weeks, then fell graduallyREVIEW 519 and became steady. There is but little doubt that this effect was caused by the ageing of the glass, a phenomenon identical with the ageing of mercury thermometers. w. P. s. *@*+I+@