140 Proceedings of the 



Honey and sugar of milk have the same properties, which, how- 

 ever, have never been observed, except in saccharine substances. 

 Potash and soda may be substituted for lime in this experiment 

 with a similar effect, except that their faculty of dissolving 

 is greater, whereas that of barytes and strontia is much less. 

 Gum does not produce the same effect as sugar : that substance, 

 when dissolved by water, is not precipitated by the alkalies and 

 earths which we have just mentioned, but if a deutoxide of 

 copper, in a state of hydrate, be added, a flaky insoluble precipitate 

 of gum and oxide of copper is formed. When there exists in the 

 solution a small quantity of saccharine matter in addition, it re-acts 

 immediately on the excess of oxide, and of copper, which has been 

 added, dissolves it, and gives a blue colour to the solution. In 

 order, therefore, to detect the existence of gum and saccharine 

 matter in any substance which contains both, it is sufficient to add 

 potash and caustic lime to the solution, and then apply hydrate of 

 copper to it. The mucilage found in a decoction of linseed pro- 

 duces the same effects as gum; and as the solution becomes slightly 

 tinged with blue, it is evident that it contains saccharine matter. 

 If the solution be acted on by heat, the effects are different. If a 

 solution of sugar, potash, and deutoxide of copper, in water, be 

 heated to the boiling temperature, the blue colour changes succes- 

 sively to green, yellow, orange, and finally to red, and then all the 

 deutoxide is changed into protoxide. If oxide of copper be then 

 added gradually, until there is no longer any protoxide formed, all 

 the sugar is decomposed, and nothing remains in the solution but 

 carbonate of potash and a small quantity of acetate of the same 

 base. The saccharine matter of milk, which, when cold, acts on 

 copper and potash in the same manner as common sugar, acts dif- 

 ferently when heated. The deutoxide of copper passes first to a 

 state of protoxide, and is then reduced to a metallic state. The 

 oxides of gold, silver, and platina, submitted to the same tests as 

 the oxide of copper, are reduced to a metallic state, while the oxides 

 of iron, zinc, and cobalt do not undergo any change. The 

 deutoxide of mercury is reduced to a metallic state by potash and 

 the saccharine matter of milk ; it then, in consequence of the water 

 which is interposed between the parts, presents itself under the 

 form of paste. Under this form, the mercury may be applied to 

 glass without the necessity of using tinfoil ; it is sufficient to spread 

 the paste in a very thin layer, and heat the glass slightly, to remove 

 the water which is interposed. Lime, barytes, and strontia, when 

 acting by means of heat on the deutoxide of copper and saccharine 

 matter, do not form compositions similar to those of the alkalies. 

 Lime, for instance, does not convert the deutoxidp into a protoxide, 

 or a metallic state ; it occasions a precipitate of an orange-yellow 

 colour, formed of the protoxide of copper and lime. In the same 

 manner, proto-cuprates of barytes and strontia are precipitated. 

 These are the principal results of M. Becquerel's experiments, which 



