170 CARNEGIE INSTITUTION OF WASHINGTON. 



tions caused by slightly incorrect interfacial prism angles. From these curves 

 the sensitiveness of the several optical methods which have been proposed for 

 testing the accuracy of prism angles by the use of transmitted light rays can 

 be detected directly and the suitability of each method thereby ascertained. 



(412) The system copper: cupric oxide: oxygen. H. S. Roberts and F. Hastings Smyth. 



J. Am. Chem. Soc, 43, 1061-1079 (1921). 



At temperatures below 1060° CuO dissociates with the formation of solid 

 CujO and O2 gas, and CU2O with the formation of solid Cu and O2 gas; solid 

 solution, if it occurs at all, is so limited in extent as to be without apprecia- 

 ble effect on the dissociation pressures. Thus the system as a whole is of a 

 very simple type. 



Pure Cu melts at 1082.8"; CU2O at 1235° under an oxygen pressure of 0.6 

 mm. of mercury. Because of the high pressure necessary to prevent dissocia- 

 tion, the melting-point of CuO could not be determined; it probably lies 

 above 1260° with a dissociation pressure of, perhaps, several thousand atmos- 

 pheres. There is a eutectic at 1062°, about 0.013 mm. of mercury, 3.4 per 

 cent CU2O and 96.6 per cent Cu by weight; a eutectic at 1080.2°, 402.3 mm. 

 of mercury, 29.5 per cent CuO and 70.5 per cent CugO by weight; another 

 quadruple point at 1195° and about 0.66 mm. of mercury where sohd CU2O 

 is in equihbrium with gas and with two immiscible liquids whose composition 

 lies between Cu and CU2O. 



At 900° the dissociation pressure, i. e., the oxygen pressure under which 

 CuO and CU2O may coexist, is 12.6 mm. oif mercury; as the temperature rises, 

 this pressure increases to 402.3 mm. at the eutectic temperature. At still 

 higher temperatures the two oxides and oxygen can no longer exist in equi- 

 librium, and one or the other disappears, giving place to a liquid whose com- 

 position is intermediate between CuO and CU2O. Where CuO remains as the 

 sohd phase, the equilibrium pressure increases with rising temperature, more 

 and more rapidly, reaching 44,700 mm. of mercury at 1232.5°, the highest 

 temperature investigated. Where CujO remains, the equihbrium pressure 

 decreases with rising temperature until it reaches 0.6 mm. of mercury at 1235°, 

 the melting-point of CU2O. 



We succeeded in determining only one of the P-T curves between Cu and 

 CU2O : the dissociation pressure curve between the CU-CU2O eutectic and the 

 quadruple point at 1195°. From the latter point the dissociation pressures 

 follow a curve, which finally joins and becomes continuous at the melting- 

 point of CU2O with the P-T curve for Cu20-Liquid-02 described in the pre- 

 vious paragraph. 



Since the system is not compUcated, it was thought worth while to present a 

 mathematical discussion of the various curves and to calculate, from the data, 

 the heat of dissociation and the free energy changes of CuO at 1000°, as well 

 as the heat of fusion of CujO. 



(413) Diffusion in sihcate melts. N. L. Bowen. J. Geo!., 29, 295-317 (1921). 



The rate of diffusion in certain silicate melts has been determined experi- 

 mentally by permitting diffusion against gravity of a heavy liquid into a lighter 

 liquid. The concentration curves found are not coincident with any theoreti- 

 cal curve calculated on the basis of a constant value of the diffusivity, but 

 can be interpreted on the assumption that the diffusivity varies with concen- 

 tration and is less for concentrations corresponding to more viscous liquids 

 than for those corresponding to less viscous liquids. Taking as representa- 

 tive of the "average diffusivity" the amount of material which penetrates into 

 the upper layer, the following values of the average diffusivity (k) were found : 

 for diopside into Ab2Ani, A; = 0.015; for diopside into AbiAni, A; = 0.14 to 0.3, 



