COMMUNICATIONS TO THE EDITOR
2248
Vol. 62
THE STRUCTURE AND PROPERTIES OF GLASSES CONTAINING BORON
boron atoms to be surrounded by but 3 close oxygen neighbors. Sir : A computation of the relative amounts of B’ I n a series of papers to be published in the (with 4 oxygen neighbors) and B” (with 3) is Journal of the Optical Society of America, a large possible on the basis of the following assumptions. amount of evidence is presented to show that (1) If (Nsi N B ) is less than one-half, every the volume, the refraction, and the dispersion boron atom is surrounded by 4 oxygens; (2) of that amount of a silicate glass which contains if (Nsi N B ) is greater than one-half, every one gram atom of oxygen are simple additive func- oxygen atom has two silicon or boron neighbors. tions of the ratios ( N M )of the numbers of atoms Assuming also (3) that the values of bsi and of the “metallic” elements to the number of atoms csi depend on the range of (Nsi N B ) , rather of oxygen, in accordance with the equations than on NSi alone, cB#, cB”, aBl and aBn values Vo k + bsi Csi Nsi Z’CM N M have been deduced which give fair agreement (%A - I)vo = Ro,A = Z U M , ~Nhi with experiment, much better than is obtained on (%A, - m J V o = DO,AIA> = Z(LZM,A,- UMAJNM the assumption that the boron atoms are all alike, In general, the a M and CM constants do not as regards their effect on the volume and refracvary with the composition. The constants bsi tion of glasses. and csi, however, are different for different ranges There is some indication that the actual of NS. The constant k is small, or zero, and seems number of B’ atoms is somewhat greater than NB) near to depend on the laboratory in which the data that calculated, especially for (Nsi originate, presumably on the annealing technique. 0.50, with NB large compared with Nsi. This would account for the large deviations from the straight line of the points on the right-hand side of 6.0 the accompanying figure. The discrepancy might be expected to be less, the better the annealing.
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L. HUGGINS MAURICE KODAK RESEARCH LABORATORIES ROCHESTER, NEWYORK RECEIVED JULY 2, 1940
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THE APPARENT MOLECULAR SHAPE AND MOLECULAR WEIGHT OF PROTEINS, FROM VISCOSITY AND DIFFUSION MEASUREMENTS
Sir:
0.12 0.20 0.28 0.36 As a part of an investigation of the molecular NB, for ( N s , N ~ ) < 0 . 5 0 NB‘ = shape and weight of native and denatured pro~-~NS,-~N forB (Nsl , NB)> O 50 teins, we have carried out viscosity and diffusion Fig. 1.-Data by Turner and co-workers, (Ns, NB)> 0.435: 0, Na20-B203; 0 . Na20-B203-Si02, 0,Naz& measurements of some undenatured proteins, B20a-Si02(-Ca&A120s-Fe~08) ; X , N ~ ~ O - K ~ O - C ~ O - B Zunder O~ carefully controlled experimental condiSiOz(-A120s-Fe20s).
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Boron-containing glasses do not obey these simple equations without modification. The contribution of the boron to the volume (or the refraction or the dispersion) depends not only on NBbut also on Nsi. From our present knowledge of atomic and ionic radii and of the crystal structures of boron-containing compounds, we should expect that in glasses in which both Nsi and N B are small (i. e., in which oxygen atoms are present in relatively large proportions), most or all of the boron atoms would be surrounded tetrahedrally by four oxygen atoms. On the other hand, with large Nsi and N , we should expect some of the
tions. Our viscosity measurements were confined to low protein concentrations, i. e., between 1 and 15 mg. per cc. The specific viscosities of the proteins investigated are independent of the velocity gradient and linear with respect to the protein concentrations up to about 8 mg. per cc. The diffusion measurements were carried out as described previously.lp2 The apparent shapes of the protein molecules, assuming negligible hydration, were calculated from their specific viscosities with the equation derived by Simha,3 without the approximation given previously.
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(1) Neurath and Saum, J. Bid. Chem.. 188,437 (1939). (2) Neursth and Cooper, ibid.. in press (1940). (3) Simha, J . Phys. Chem., 44, 25 (1940).
