638 EEPORT— 1888. 



any evidence of free caustic lime, Ihe author considered lie was justified in drawing 

 tlie inference that silicate of lime was present, this body beinj^ the result of direct 

 combination between lime and sand in the course of mauy centuries. 



Samples of a London mortar about a hundred years old and another of recent 

 date contained M per cent., or less, of soluble silica, that is, only one-tenth of the 

 amount now actually found in the Roman mortar analysed. 



For full particulars of composition and analytical details see the ' Chemical 

 News ' of October IS, 1888, p. 189. 



G. 0)1 the Bate of Solution of Copper in Acids. By V. H. Veley, M.A. 



From time to time accounts of experiments have been published on the rate of 

 solution of metals in acids. In most eases a piece of metal of more or less regular 

 surface is placed at the bottom of a suitable vessel, dilute acid poured thereon" and 

 the rate measured at which the hydrogen or other gas is evolved. It is obvious 

 that the measured result is one of very mixed causes, the separate effect of which 

 has not been duly taken into account. Thus the rate at which hydrogen is given 

 off from redistilled zinc and dilute sulphuric acid will depend inte7- alia on (i) the 

 surface of metal exposed ; (ii) the concentration of the acid ; (iii) the rate of 

 diffusion of the solution of salt formed in the acid liquid. Of these only (i) can be 

 approximately constant, while (ii) and (iii) are indeterminable variables. 



The author has made a series of experiments on the rate of solution of spheres 

 of_ electrolytic copper, made from oue block, in solutions of potassium bichromate 

 acidulated with sulphuric acid under such conditions that not only are fresh sur- 

 faces of the copper continually exposed, but also the dissolving liquid in the imme- 

 diate vicinity of the metal continually renewed. At the end of definite intervals 

 of time the loss in weight of the sphere is determined, and the alteration in area 

 calculated by a measurement of the axes of the sphere. The mass dissolved per 

 unit area is taken as the measure of the rate of solution. 



As a preliminary step it was ascertained that, under the same conditions, 

 different spheres of copper dissolved at the same rate. 



Experiments thus far have shown that the difference of the logarithm of the 



M 

 factor r (M = mass, A = area) is constant for a constant difference of temperature. 



But, apparently, the value of this factor is proportional only within certain limits 

 to the concentration ; thus, although with greater or less concentration the mass 

 dissolved is greater or less, yet this variation proceeds ^:>e?- saltum, and not in direct 

 proportion, even though a large excess of dissolving reagents was in all cases 

 used. 



The rate of solution is also dependent upon the rate of movement of the 

 metallic sphere in the acid ; throughout the experiments this has been kept constant 

 by various mechanical arrangements. 



7. Recovery of the Ammonia and Chlorine in the Ammonia-soda Process. 



By F. Bale. 



If ammonium chloride be volatilised, and its vapour passed over or through 

 heated metallic oxide, at a temperature of 400° C. or higher, the ammonia which 

 is evolved is partially decomposed in its passage over the heated oxide, and this to 

 the extent of from 25 to 50 per cent, of the ammonia evolved. 



If, however, the ammonium chloride be intimately mixed in powder with 

 metallic oxide in powder, as the oxide of manganese (which I prefer), and the 

 mixture then gradually heated, the ammonia is gradually and completely evolved 

 at a temperature of 130° 0. to 325° C. without the loss mentioned above by the 

 method of volatilisation of the ammonic chloride. Most of the ammonia is here 

 evolved between 130° and 200° C. 



In this method of mixtures, if the temperature of the residue left after the 

 evolution of the ammonia be kept below 350° 0. and cold and dry air be passed 



