cal formulae resulting from his own analysis of these different sub- stances.
His inquiries into the constitution of ordinary litmus, which form the last division of his subject, lead him to the conclusion that that substance contains the principles designated by him as Erythrolein, Erythrolitmine, Azolitmine, and Spaniolitmine ; and that the colour- ing constituents of litmus are, in their natural condition, red ; the blue substances being produced by combination with a base, the bases in that of commerce being lime, potass, and ammonia ; and there is mixed up in the mass a considerable quantity of chalk and sand. The details of the analyses of these several substances, and the re- sulting chemical formulae representing their constitution, are then given.
The concluding section of the paper is occupied by an inquiry into the decoloration of the bodies which exist in archil and in lit- mus. The latter of these, the author concludes, is reddened by acids, in consequence of their removing the loosely combined ammonia by which the blue colour is produced ; and the so-called hydrogen-acids liberate the colouring matter by their combining with the alkali to form bodies (either chlorides or iodides), with which the colouring matter has no tendency to unite. Hence it appears that the redden- ing of litmus is no proof that chloride of hydrogen is an acid, and that the double decomposition which occurs is the same in principle, whether hydrogen or a fixed metal come into play. After detailing the blanching effects of other deoxydizing agents on the colouring matter of litmus, and the action of chlorine on orceine and azolitmine, the author remarks, that in these actions chlorine is subjected to con- ditions different from those which determine the nature of the results with the generality of organic bodies, and that the displacement of hydrogen, so marked in other cases, does not exist in the class of substances under consideration ; but that, in reality, the products of the bleaching energy of chlorine resemble in constitution the com- pounds of chlorine which possess bleaching powers.
This paper may be viewed as a very important contribution to organic chemistry, and as highly deserving of the Royal Medal ; an award which will, doubtless, be hailed by chemists as a just encou- ragement to perseverance in skilful analytical research.
There being no paper on Mathematics coming within the stipu- lations regulating the awards of the Royal Medals, which has been deemed worthy of that for Mathematics in the present year, the Council have, in virtue of the power given to them, under these cir- cumstances, by the regulations prescribed by Her Majesty, awarded the other Royal Medal to Eaton Hodgkinson, Esq., for his paper, which was published in the Philosophical Transactions for 1840, and is entitled " Experimental Researches into the Strength of Pillars of Cast Iron, and other materials."
This paper has been esteemed by the Council to be peculiarly va- luable in a practical as well as theoretical point of view, and there- fore to deserve, in an eminent degree, the honour of a Royal Medal. It contains the results of an immense series of experiments, conducted
