272 Dr. F. W. Pavy. On the Volumetric Estimation [June 19. 



others or alone, then we shall get an excess in the reversal of the lines 

 special to that particular kind of vapour given off. 



It is remarkable from this point of view that I have only succeeded 

 in constantly reversing a triplet in the case of manganese, and that I 

 have only succeeded in reversing a triplet of iron on one or two occa- 

 sions only. Comparing these results with those obtained in the case 

 of Na, K, Ca, &c, we have here an indication of a considerable phy- 

 sical difference between the metals of the alkalies, for instance, and 

 those of the iron group. 



It is also suggested as a result of the application of this new method 

 of experimentation, that in the case of a considerable number of 

 chemical substances not only the line spectrum is compound in its 

 origin, as I suggested many years ago, but that a large number of the 

 lines is due to molecular groupings of considerable complexity, which 

 can be kept out of the reaction by careful low temperature distillation. 



Whether these higher molecular groupings are merely larger phy- 

 sical aggregates or whether they be compounds in a stricter sense, 

 hydrides for instance, it may take some time to determine ; but it is 

 obvious that however this may be, the finer vapours may exist uncon- 

 taminated with the grosser ones in the incandescent atmosphere of a 

 star ; and I know of no reason why the molecules of such fine vapours 

 should not combine with each other, and if, for the sake of argument, 

 we assume that some of the so-called chemical elements may be thus 

 compounded of those finer vapours which we know to exist in the 

 atmospheres of the hottest stars, then we may expect to find the high 

 temperature spectra of these so-called elements to consist of a com- 

 plication of lines, due partly to the complex molecules themselves and 

 partly to the finer vapours in question. 



XXVIII. " Supplementary Note on the Volumetric Estimation 

 of Sugar by an Ammoniated Cupric Test giving Reduction 

 without Precipitation." By F. W. Pavy, M.D., F.R.S. 

 Received June 19, 1879. 



In a communication published in the " Proceedings of the Royal 

 Society " (vol. xxviii, p. 260), I drew attention to the employment of 

 an ammoniated cupric liquid for the volumetric estimation of sugar. 

 Instead of giving an altogether new formula for this liquid, I re- 

 commended it to be prepared from Pehling's solution with the addition 

 of a certain volume of ammonia and of water. Under the method of 

 analytical procedure adopted in my laboratory, which consisted in 

 running in the liquid pretty quickly from the burette to near the 

 required point, and then dropping it in slowly, the amount of soda 

 contained in Fehling's solution proved sufficient to give accurate 



