Page:Proceedings of the Royal Society of London Vol 4.djvu/155

Rh Formation of Alkaline and Earthy Bodies, with reference to their presence in Plants, the Influence of Carbonic Acid in their genera- tion, and the equilibrium of this gas in the atmosphere." By Ro- bert Rigg, Esq.^ Communicated by the Rev. J. B. Reade, M,A., F.R.S.

The object of the author, in the present memoir, is to show that the solid materials which compose the residual matter in the analy- sis of vegetable substances, and which consist of alkaline and earthy bodies, are actually formed during the process of fermentation, whe- ther that process be excited artificially, by the addition of a small quantity of yeast to fermentable mixtures, or take place naturally in the course of vegetation, or of spontaneous decomposition. His experiments also tend to show that this formation of alkaline and earthy bodies is always preceded by the absorption of carbonic acid, whether that acid be naturally formed or artificially supplied. He finds, also, that different kinds of garden mould, some being calca- reous, others siliceous, and others aluminous, exposed in retorts to atmospheres consisting of a mixture of carbonic acid gas and com- mon air, absorb large quantities of the former, combining with it in such a manner as not to afford any traces of this carbonic acid being disengaged by the action of other acids. He considers the result of this combination to be the formation of an alkaline body, and also of a colouring matter. This combination takes place to a greater extent during the night than during the day ; and in gene- ral, the absorption of carbonic acid by the soil is greatest in pro- portion as it is more abundantly produced by the processes of vege- tation ; and conversely, it is least at the time when plants decom- pose this gas, appropriating its basis to the purposes of their own system. Hence he conceives that there is estabhshed in nature a remarkable compensating provision, which regulates the quantity of carbonic acid in the atmosphere, and renders its proportion constant.

A paper was also read, entitled, " Note on the Art of Photogra- phy, or the application of the Chemical Rays of Light to the pur- poses of Pictorial Representation." By Sir John F. W. Herschel^ Bart., K.H., V.P.R.S., &c.

The author states that his attention was first called to the subject of M. Daguerre's concealed photographic processes, by a note from; Captain Beaufort, dated the 22nd of January last, at which time he was ignorant that it had been considered by Mr. Talbot, or by any one in this country. As an enigma to be solved, a variety of processes at once presented themselves, of which the most promising are the following; 1st, the so-called de-oxidizing power of the chemical rays in their action on recently precipitated chloride of silver; 2ndly, the instant and copious precipitation of a mixture of a solution of muriate of platina and lime-water by solar light, forming an insoluble compound, which might afterwards be blackened by a variety of agents ; 3rdly, the reduction of gold in contact with deoxidizing agents ; and, 4thly, the decomposition of an argentine compound soluble in water, exposed to light in an atmosphere of peroxide of chlorine, either pure or dilated.