July 4, 1919] 



SCIENCE 



25 



a calomel electrode; ferric iron is reduced with 

 stannous chloride after which the excess of the 

 reducing agent and the ferrous iron are titrated 

 together, the curve of potential against quantity 

 of diehromate showing two points of inflection be- 

 tween which is the amount of diehromate corre- 

 sponding to the iron. Small amounts of ferrous 

 iron can be determined directly in ferric salts and 

 similarly ferric iron directly in ferrous salts: 

 other applications of the method are given. 



The effect of strain on soluhility (lantern) : J. 

 C. HosTETTEK. It is possible that fluctuating tem- 

 perature and, perhaps, some indirect effects brought 

 about by pressure may account for the solidifica- 

 tion of crystals compressed in contact with their 

 solution by loosely fitting pistons— as found by 

 James Thomson, Le Chatelier and Spring — with- 

 out the necessity of postulating large increases in 

 solubility due to non-uniform pressure. In pre- 

 liminary experiments, individual crystals were sub- 

 jected to stress at constant temperature by direct 

 loading, and the effect on the concentration of the 

 surrounding solution studied, by measuring the 

 electrical conductivity. No change in concentra- 

 tion was found. The test was sufficiently sensi- 

 tive to indicate that the effect of non-uniform 

 pressure is much less than that produced by the 

 same pressure acting uniformly. However, in 

 another series of experiments in which an un- 

 loaded crystal was placed alongside a loaded cry- 

 stal, the former grew at the expense of the latter, 

 showing that a very slight increase of solubility 

 was produced by the stress. The method of load- 

 ing the crystals has a large influence on the ef- 

 fects found, thus indicating the importance of 

 the stress distribution. The experiments of 

 Becker and Day on the linear force of growing 

 crystals are cited as indicating the stability of a 

 crystal in its solution, even when subjected to 

 pressure. In their experiments loaded crystals 

 were found to lift the load during growth, al- 

 though the pressures on the supporting edges of 

 the crystals were finally of the order of magni- 

 tude of the crushing strength of the crystal. The 

 evidence so far obtained indicates that the effect 

 of strain on solubility is a second order effect. 



A method of growing large perfect crystals from 

 solution (lantern) : EoT W. Mooee. This method 

 consists briefly of placing or hanging a small seed 

 crystal or several of them in a nearly-saturated so- 

 lution, cooling the solution until it is very slightly 

 supersaturated, and maintaining a state of slight 

 supersaturation by slowly cooling the solution, 

 with the temperature regulated within very 



narrow limits. Under these conditions, the seed 

 crystals will build out to form perfectly devel- 

 oped, clear crystals, and these will continue to 

 grow clear and perfect as long as a state of slight 

 supersaturation is maintained. By this method, 

 crystals of Eochelle Salt have been produced that 

 are three inches or more long and two inches thick, 

 perfectly clear and with all surfaces and angles 

 perfectly developed. This method should be ap- 

 plicable to any substance which crystallizes from 

 solution either in water or other solvents, pro- 

 vided the solubility varies considerably with the 

 temperature. 



Action of nitrogen and hydrogen mixture on 

 steel at high pressure and temperature (lantern) : 

 R. O. E. Davis. When subjected to an atmosphere 

 of nitrogen and hydrogen at high pressure and 

 temperature of 500° C. for some weeks carbon steel 

 shows a marked change in physical characteristics; 

 it ds probable that a compound is formed between 

 the iron and the gases. 



Comparative tests of palau and rhotcmium ware 

 as substitutes for platinum laboratory utensils 

 (lantern) : L. J. Gurevich and E. Wichers. A 

 series of tests has been carried out at the bureau to 

 determine the suitability of the palau and rho- 

 tanium alloys as substitutes for platinum labora- 

 tory ware. The tests were of two types, the aim 

 being to determine the resistance of the materials 

 to chemical reagents, and their behavior on heat- 

 ing. These tests indicate that rhotanium "A" 

 ware is superior to platinum ware both of high 

 (2.4 per cent.) and low (0.6 per cent.) iridium 

 content in respect to its resistance to loss on heat- 

 ing. The losses on treatment with acid, after 

 heating, are about equal. Grade "A" ware com- 

 pares favorably with platinum in resistance to 

 boiling hydrochloric and hydrofluoric acids, to 

 boUing 20 per cent, sodium hydroxide, and to 

 fusion with sodium carbonate in a mufSe, and with 

 potassium pyrosulphate. It is superior to plati- 

 num in resistance to the action of boiling sul- 

 phuric acid, and inferior in its resistance towards 

 boiling concentrated and dilute nitric acids, boil- 

 ing 10 per cent, ferric chloride solution, and for 

 fusions with sodium hydroxide. The only objec- 

 tion that may be raised to its use is the rather 

 low melting point of the alloy, which makes it 

 impossible to blast or strongly heat the ware with- 

 out melting it. As far as resistance to loss in 

 weight on heating to 1,200° C. is concerned, rho- 

 tanium "C" and palau wares are about equal, if 

 not slightly superior, to platinum ware containing 

 0.6 per cent, iridium. They are surely superior to 



