838 REPORT— 1898. 



conuected that, when the air had been exhausted from the flask, vapour from the 

 boiling- carbon tetrachloride took its place in the interstices of the crystals. Then, 

 by tilting the vessel, the llask was tilled with liquid tetrachloride. " On removing- 

 the flask the stopper was inserted as before. Eleven determinations of the density 

 of quartz show a maximum divergence of -03 per cent. 



4. To remove moisture retained on the surface of the crystals, a current of dry 

 air was passed through the flask till on passing out it yielded no moisture to 

 phosphorus pentoxide. The apparatus -was then exhausted, and carbon-tetra- 

 ohlorido was admitted suflicient to cover the crystals. The flask was then filled up 

 as before. Four determinations by this method of the density of K-CO^ show a 

 maximum divergence of -04 per cent. 



8. The Equivalent Replacement of Metals. By Professor Frank Clowes, 



D.Sc, Lond. 



It has long been known that when iron is immersed in a solution of cupric 

 sulphate metallic copper is deposited, and an amouut of iron passes into solution 

 -*vhich is exactly able to combine with the sulphate radicle liberated from the 

 cupric sulphate. The weights of copper and of iron which combine -with the same 

 weight of sulphate radicle have been determined by carrying out the process 

 quantitatively. These weights are chemically equivalent to one another, for they 

 are able to combine with the same weight of the acidulous radicle. 



In the case just cited the chemical change appears, at ordinary temperature 

 and with dilute cupric solution, to follow the simple course stated. But attempts 

 to extend this direct method of ascertaining the relative equivalents of metals 

 cease to be direct in certain cases, owing to the complicated nature of the reaction.-^ 

 ■which occur. 



My attention was drawn to such a complication in the case of the action of 

 magnesium on cupric sulphate solution, and the nature of the reaction was thei: 

 investigated by R. M. Caven, B.Sc, and myself. Commaille,' Kern,'- and Vitali,-' 

 had drawn attention to the facts that during the action of magnesium on cupiic; 

 sulphate solution cuprous oxide was deposited with the metallic copper, and hydro- 

 gen was evolved. These facts prove that the copper equivalent of magnesium 

 cannot be obtained by simply weighing the magnesium which passes into solution 

 and the deposit -^-hich was formed during the process. But we proceeded to make 

 a fuller examination of the nature of the reaction, and to show that when it was 

 quantitatively carried out the products enabled us to calculate the equivalents of 

 magnesium and copper. 



Having obtained practically pure materials, we proceeded to study the reactions 

 when the conditions were varied by employing hot or cold and strong or weak 

 cupric sulphate solutions. We were met -\vith the initial difficulty that cupric 

 sulphate solution deposits a basic salt when it is boiled : this salt we separated 

 and found to correspond in composition and properties to the formula 4CuS0j. 

 7Cu(0H).,. 11.^0. Pickering had separated a similar salt, to which he attributed 

 the formula 60uO.2S0...5H,p. Owing to the deposition of this salt complicating 

 the products, we avoided actual ebullition in our experiments. 



The action is most simple -n-hen the magnesium is immersed in a hot strong 

 solution of cupric sulphate. Hydrogen is briskly evolved, a chocolate-coloured 

 deposit forms, and gi-een flakes are produced which disappear before the reaction is 

 completed. Treatment of the brown deposit with dilute hydrochloric acid yields 

 colourless cuprous chloride solution and a small residue of metallic copper. The 

 h3'drogen evolved was collected and measured, the metallic copper was weighed 

 directly, and the amount of cuprous oxide was determined by dissolving it in 

 hydrochloric acid and determining the amount of cuprous chloride thus formed by 



' Comptes Ttcndus, Ixiii. p. 556. 

 - Clicm. Xovs, xxxiii. p. 236. 

 ' Journ. Chem. Soc, Ixx. p. 419. 



