316 Intelligence and Miscellaneous Articles. 



adsorbed film of liquid, which has become almost solid, the mag- 

 nitude of the pores of the " precipitate-membrane " through which 

 the diffusion takes place is again determined ; while the thickness 

 of the adsorbed film may depend upon the velocity with which the 

 insoluble substance of the membrane has been produced. 



This theory of diffusion through sieve-like precipitate-mem- 

 branes is especially supported by experiments with a watery 

 solution of tannic acid and so-called /3 gelatine — that is, ordinary 

 concentrated gelatine solution which has been kept for a long time 

 heated to 100° 0. and has thereby acquired the property of remain- 

 ing liquid even after cooling. A drop of this solution, cooled upon 

 a glass rod, brought into a solution of tannic acid, forms, in the 

 course of an hour or two, a little sac filled with fluid, which 

 gradually grows larger until finally it bursts or again shrivels up. 

 M. Traube thinks that here a precipitate- membrane of insoluble 

 tannate of gelatine is formed, through the pores of which no 

 tannic acid, but only water, can come from the outside to the 

 gelatine solution in the interior. 



I have left for twenty-four hours a drop of warm (j gelatine to 

 dry adhering to the lower aperture of a short, light funnel blown 

 from a clean glass tube, and then placed the funnel as a float 

 on a five per cent, solution of tannic acid. After three hours a 

 sac, filled with fluid, had formed out of the gelatine, which was 

 bounded by air in the interior of the funnel, and was penetrated 

 by a glass thread introduced into the upper opening of the funnel 

 without injuring the bottom part adjacent to the tannic acid. A 

 portion of the fluid ascended out of the interior of the sac, by the 

 capillary attraction of the glass thread ; and, emptied into a watch- 

 glass, it gave, with chloride of iron, a deep-black colouring. It 

 appears that the gelatine sac contained in its interior at first much, 

 but after a longer diffusion a less quantity of tannic acid. Thus, 

 in contradiction to the theory of the sieve-like precipitate-mem- 

 branes, tannic acid penetrated from without into the interior of 

 the precipitate-membrane covering the gelatine ; and the process of 

 the diffusion of gelatine and tannic-acid solution is much more com- 

 plicated than it is conceived to be by that theory. — Poggendorff's 

 Annalen, 1877, No. 1, vol. clx. pp. 118-123. 



ON COSMIC VULCANISM. BY M. TSCHEEMAK. 



The present is in continuation of a previous paper, on the 

 probable mode of formation of meteorites, in which the opinion 

 was expressed that, judging according to our present knowledge, 

 all stellar systems in their development pass through a volcanic 

 phase. 



The crater-form of the lunar mountains, the eruptive phenomena 

 in the sun, the change of brightness of stars, the nature of meteor- 

 ites (which for the most part resemble volcanic tufas) are all facts 

 which, it may be conjectured, are connected by a common bond. 

 But the attempt to bring these perceptions under one point of 

 view with our experience of terrestrial volcanoes fails, if based on 

 those hypotheses which have recently come to the front. 



