368 Royal Society. 



without decomposition. The intensity of its action upon water 

 varies according to the manner in which the two bodies are brought 

 together. When poured rapidly into a large quantity of cold water, 

 a portion of it sinks to the bottom, and only gradually dissolves as 

 a mixture of hydrochloric and sulphuric acids. When a small 

 quantity of water is added to the compound, the same decomposition 

 takes place with explosive violence. The acid dissolves chloride of 

 sodium on the application of a gentle heat with evolution of hydro- 



NaQ 

 chloric acid, giving rise to a compound of the formula SOj . When 



CI 

 poured upon pieces of melted nitre at the atmospheric temperature, 

 an effervescence takes place with evolution of a colourless vapour 

 which possesses in a striking degree the odour of aqua regla. This 

 vapour may be dissolved in various liquids, and when decomposed 

 by water, yields nitric and hydrochloric acids. It is doubtless 

 chloro-nitric acid, NOjCl. In like manner the chlorides of other 

 inorganic acid radicals may be obtained, as from chlorates, perchlo- 

 rates, sulphites, &c., but of these and other reactions I beg leave to 

 defer any further account until the experiments now in hand are 

 more advanced. 



From the general resemblance of properties and identity of boiling- 

 point of the chloro-hydrate with a compound discovered by Rose, 

 and described by that eminent chemist as possessing empirically the 

 composition Sj Oj CL, I was led to suspect that the two might in 

 reality be identical, which of course would require the addition of 

 the elements of water to Rose's formula, and several experiments I 

 have performed afford strong confirmation of that identity. The 

 same compound is obtained by the action of dry hydrochloric acid 

 on anhydrous sulphuric acid ; and finally, I may mention that 

 Mr. Railton obtained a small quantity of the same substance some 

 weeks ago in my laboratory by the action of platinum-black at a 

 high temperature on an imperfectly dried mixture of chlorine and 

 sulphurous acid. 



As regards the successive transformations effected in the penta- 

 chloride, I have observed the formation of Wurtz's oxychloride (the 

 tribasic chloro-phosphoric acid (PO CI3)), and also of a compound 

 boiling above 145°, probably PO^ CI. Hydrated phosphoric acid is 

 always found unless the amount of peatachloride added is very 

 great. 



March 9.— Thomas Bell, Esq., V.P., in the Chair. 



The following paper was read : — 



" On a new and more correct method of determining the Angle 

 of Aperture of ]\Iicroscopic Object-Glasses." By William S. Gillett, 

 Esq., M.A. 



The very large apertures assigned to the more recent microscopic 

 object-glasses drew the author's attention some time since to the im- 

 portance of testing the accuracy of the method employed to deter- 

 mine their amount. 



