ketonic ethers and of the fatty acids lays open a direct path, through the beautiful reactions either of Mendius or Friedel, to corresponding alcohols.

In conclusion, there can be no doubt that the reaction which forms the subject of this paper is capable of a very wide extension, and that by its means we shall be able to ascend many of the well-recognised homologous series. In future communications we hope to give the results of its extension to the alcohols and ethers, and to the benzoic series of ethereal salts.

XLI.-Action of Acids upon Metals and Alloys.

By DR. CRACE CALVERT, F.R.S., and RICHARD JOHNSON, F.C.S.

IT has frequently occurred to us, in the course of our investigations into the physical properties of metals and alloys, that it would be interesting both in a scientific and practical point of view, if we were carefully to examine the action of some of the acids upon them. We, therefore, submitted copper, zinc, and tin, and the two classes of alloys which are obtained from these metals, viz., brasses and bronzes, to the action of sulphuric, nitric, and hydrochloric acids.

In this series of researches we have followed the same plan as when we experimented upon the "conductibility," the "specific gravity," &c., &c. of metals and alloys; viz., we first examined the action of these acids upon the pure metals, and afterwards upon the alloys composed of the pure metals melted together in equivalent and multiple proportions.

Our experiments having been very numerous, and therefore, having extended over a long period of time, we have deemed it advisable to divide our paper into two parts.

First-The action of sulphuric acid upon zinc, copper, and tin, and of nitric and hydrochloric acids on the same metals.

Secondly-The action of the same acids upon their alloys, viz., brasses and bronzes.

On the marked influence which an Oxidized Surface has on the subsequent action of Sulphuric Acid of various strengths on Zinc.

Before entering into the details of our experiments, it is necessary that we should state, that it was only after considerable time and experience that we were able to determine the exact conditions under which we were to operate, if we wished to obtain constant and correlated results, owing not only to the extreme difficulty attending the preparation of perfectly pure sulphuric acid and a few ounces of pure zinc, but especially to the irregularity of the action of sulphuric acid on zinc, depending, as we observed, upon the peculiar state of its surface. Thus we found that cubes which had been made of the same zinc, but at different times, were acted upon more or less by the same acid when placed under the same circumstances; and these observations gradually led us to the discovery of a curious fact, viz., that a perfectly clean surface of zinc will become, after a few days, sufficiently oxidized by contact with air to modify in a very marked degree the action of sulphuric acid upon it. Thus, if a cube of zinc recently filed is placed in sulphuric acid diluted with 9 eq. water, the action may be considered as null; whilst if the same cube be gently heated in contact with the air and allowed to cool, and be then placed in the same strength of acid, the attack is 10 times greater, as proved by these results.

On the Action of Sulphuric Acid of various Strengths on Zinc.

In looking over the table following these remarks, and containing our results on the action of various strengths of sulphuric

acid on pure zinc with an unoxidised surface, it will be observed, firstly, that they are contrary to the general view entertained by chemists of the action of sulphuric acid upon that metal, for this acid has no action at ordinary temperatures on zinc; also that it requires a temperature of 130° C. before concentrated acid begins to show any marked action, and that it is only at 150° C. that the action of sulphuric acid with 1 and 2 equivalents of water, is fully developed. Secondly, on perusing our results, the following curious facts will be observed, viz., that mono- and bi-hydrated sulphuric acids exercise a comparatively limited action on zinc at a temperature of 130° C. as compared with that of the tri-hydrated acid; thus, whilst SO,,HO and SO3,2HO will dissolve only respectively 125 or 2366 grammes zinc on a square metre surface, SO3,3HO) will in the same space of time dissolve 9860 grammes or 7 to 8 times the amount. Further, the same extraordinary difference of action of these various strengths of acids is maintained when their temperature is raised to 150° C.

A similar difference of action is observed when the action of diluted sulphuric acids on the unoxidized surface of pure zinc is studied; thus when SO3,6HO acts upon such a metal, only 561.6 grammes per metre surface are dissolved in two hours, whilst SO3,7HO dissolves in the same space of time as much as 5260 8 grammes, but in this case the temperature employed was only 100° C., or that of the boiling point of the latter acid.

The reactions of sulphuric acid of different strengths upon an unoxidized surface of pure zinc, are far more complicated and interesting than chemists admit. To understand them it is necessary that they should be classed under two distinct heads, viz., the action of SO,,HO, in which case the metal is oxidized solely at the expense of the acid, sulphurous acid being produced, whilst with SO3,2HO, and especially with SO,,3HO, not only is sulphurous acid given off, but also simultaneously with it sulphuretted hydrogen.

It is interesting to observe two distinct chemical reactions taking place simultaneously; thus we have an action similar to that which sulphuric acid exercises on the metals of the alkalies or alkaline earths, giving rise to hydrogen and a sulphate of the metal, and that which sulphuric acid has, viz., on the fifth group, etc., viz., mercury, generating sulphurous acid and a sulphate of the metal.

Lastly, it will be observed on looking over the table that sul

phurous acid gradually disappears, whilst the quantity of sulphuretted hydrogen increases, until in its turn it also disappears and is replaced by pure hydrogen.

TABLE 1.

Action of Sulphuric Acid of different strengths upon pure Zinc.

Action of Sulphuric Acid on Copper.

The following is the action of 50 cubic centimetres of sulphuric acid, of different strengths, upon 1 cent. cube of pure copper, during a period of two hours, and at the temperature of 130° and 150° C.

TABLE 2.

Action of Sulphuric Acid of different strengths upon pure Copper.

These results suggest to us the following remarks: that the temperature at which copper is first attacked by sulphuric acid, SO,HO, is 130° C., and that even at a few degrees below that temperature, copper is not acted upon; further, that at 150° C., the quantity of copper dissolved by this acid under the same circumstances is nearly the double of that which SO3,2HO, SO3,3HO could dissolve, whilst SO,,4HO, have little or no action upon that

metal.

We further noticed, that the decomposition of SO,HO, by copper is far more complicated than it is generally admitted to be; for the action does not consist simply in the decomposition of the acid into oxygen which oxidizes the copper, and sulphurous acid which escapes, but the affinity of copper for oxygen is such that the whole of this gas is removed from a certain portion of the sulphuric acid, leaving free sulphur, which combines with the copper to form sulphide of copper. The reason which leads us to believe that the formation of this compound is due to the direct combination of the sulphur with the copper, and not, as in the case of zinc, to two chemical actions taking place simultaneously, is that if water were decomposed into its constituent elements, its oxygen uniting with the copper, whilst its hydrogen would com