TBANSACTIONS OF SECTION B. 



541 



This fact is made uso of in the present apparatus, a bulb containinj^ chlorine is 

 attached to the beam of a balance, and the expansion of the gas causes sulphuric 

 acid to flow from one position on the beam to another. A movement of the beam Ls 

 thus brouglit about ; this is registered by means of a pointer attached to the beam, 

 which describes a line on a rotating drum. 



The effect of change in volume of the gas, due to variations in temperature, is 

 eliminated by means of a compensating apparatus. 



8. Explosion of a Mixture of Hydrogen, Chlorine, and Oxygen. 

 By Professor H. B. Dixox, F.B.S. 



9. On the Action of Light on Dry Hydrogen and Ghlorine. 

 By Professor H. B. Dixon, F.B.S. , and J. A. Harker. 



10. On Artists' Colours. By A. P. Laurie, M.A., B.Sc. 



This investigation has been undertaken with a view to supplying artists with 

 permanent pigments, at the suggestion of Mr. Holman Hunt. Three lines of 

 inquiry are being pursued, namely, to study the methods used for the preparation 

 of colours in the loth and 16th centuries as described in the manuscripts of 

 Cennino Cennini and others ; '2, to practise the manufacture of colours ; 3, to 

 examine modern colours more especially for traces of injurious chemicals. Much 

 valuable information has been obtained, and several colours successfully prepared. 

 It has also been found that different methods are in use in the trade for making the 

 same colour ; some samples, for instance, of Prussian blue containing free sulphuric 

 acid, and of vermilion containing potassium sulphide. 



11. 



Specific and Latent Heat in relation to the combining Heats of the 

 Chemical Elements. By Dr. W. Newton. 



The figures given at present as the heat of combination of the elements only give 

 the exact amount of heat due to chemical action when the elements combining are 

 gases and the compound formed is a gas. 



Capsule. 



In other cases, where either the elements or their product are solid or liquid, 

 the figures for the beat of combination are made up of chemical heat of combination. 



