ON THE FORMATION OF HALOID COMPOUNDS. 275 



metallic and other chlorides and analogous compounds ; and it is in this 

 direction that the Committee are woi'king. 



Mr. Shenstone has already obtained results which are both interest- 

 ing and suggestive. Chlorine prepared in the ordinary manner dried by 

 exposure in contact with phosphoric oxide during several months was 

 found to very readily attack mercury — a result in accordance with 

 Cowper's observation. Nevertheless chlorine prepared in another 

 manner was found to behave differently. With the object of testing the 

 quality of chlorine prepared by heating platinous chloride in vacuo, tubes 

 of such chloi'ine, dried by contact during several hours with phosphoric 

 oxide, were opened under highly-purified recently-heated mercury : 

 although the surface of the mercury in contact with the gas was very 

 quickly tarnished, no sensible absorption occurred during many hours in 

 dayhght, but afterwards absorption took place, at first gradually, and 

 subsequently with tolerable rapidity. Several such experiments were 

 made with chlorine prepared from different specimens of platinous chlo- 

 ride, and in every case a colourless gaseous residue, not exceeding 5 per 

 cent., was obtained, which proved to be partly soluble in water, partly in 

 alkaline pyrogallate, and partly insoluble, (? Nitrogen.) The fact that 

 absorption at first took place with exceeding slowness, and subsequently 

 proceeded at a more and more rapid rate, is apparently a significant 

 indication that the interaction of chlorine and mercury is conditioned by 

 the presence of some third substance, and the importance of continuing 

 the enquiry is unquestionable. 



It is probable that the impurities in the gas from platinous chloride 

 are derived from a basic compound. Mr. Shenstone finds that platinous 

 chloride is to a slight extent volatile — a fact which is ordinarily overlooked, 

 although it has been noticed by Mr. G. Matthey ; hence the analysis of 

 the substance by the ordinary method of ignition is liable to afford falla- 

 cious results. 



Nearly 201. has ah-eady been expended, chiefly in the purchase of 

 platinum and platinum apparatus. The Committee desire to be re- 

 appointed, with a grant of ,30/., as the experiments are now being extended 

 to a number of other compounds. 



Provisional Report of the Committee, consisting of General Festing, 

 Captain Abnet, and Professor H. E. Armstrong {Secretary), 

 on the Absorption Spectra of Pure Compounds. 



The determination of the spectra of the compounds which the Committee 

 have fixed upon as essential has been continued, and several have been 

 measured and classified. The work is very laborious and can only 

 progress slowly owing to the difficulty of obtaining absolutely pure 

 compounds, and other difficulties in the photographic method employed 

 have also arisen. The Committee wish for reappointment to continue the 

 investigation. 



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