From the success of this experiment, so well authenticated, and continued for several months, I am led to be of opinion, that all blast furnaces, by a proper adjustment of such machinery as they are provided with, might greatly and advantageously increase their produce, by assuming this as a principle, viz. "That with the given power it is rather by a great quantity of air thrown into the furnace, with a moderate velocity, than by a less quantity thrown in with a greater velocity, that the greatest benefit is derived, in the smelting of ironstones, in order to produce pig iron." However, it is by experiment alone, perhaps, that we can be enabled to find out the exact relations of power, velocity, and quantity of air requisite to produce a maximum of effect *.

Experiments on Whinstone and Lava. By Sir James Hall, Bart. F.R.S. and F.A.S. Edin.We are here informed that these experiments were suggested to the author many years ago, when he was employed in studying the geological system of Dr. Hutton, by the following plausible objection to which that system appears to be liable:

Granite, porphyry, and basaltes, are supposed by Dr. Hutton to have flowed in a state of perfect fusion into their present position; but their internal structure, being universally rough and stony, appears to contradict this hypothesis; for the result of the fusion of earthy substances, hitherto observed in our experiments, either is glass, or possesses in some degree the vitreous character.

This objection, however, (continues Sir James) loses much of its force, when we attend to the peculiar circumstances under which, according to this theory, the action of heat was exerted. These substances, when in fusion, and long after their congelation, are supposed to have occupied a subterraneous position far below what was then the surface of the earth; and Dr. Hutton has ascribed to the modification of heat, occasioned by the pressure of the superincumbent mass, many important phenomena of the mineral kingdom, which he has thus reconciled to his system.

One necessary consequence of the position of these bodies seems, however, to have been overlooked by Dr. Hutton himself: I mean that, after their fusion, they must have cooled very slowly; and it appeared to me probable, on that account, that during their congelation, a crystallization had taken place with more or less regularity, producing the stony and crystallized structure, common to all unstratified substances, from the large granite, to the fine grained and almost homogeneous basalt. This conjecture derived additional probability from an accident similar to those formerly observed by Mr. Keir, which had just happened at Leith: a large glass-house pot, filled with green bottle glass in fusion, having cooled

*If Q be the quantity of a fluid, issuing in a given time through an aperture of the diameter D, V its velocity, and P the power by which it is forced through the aperture: then the area of that aperture being as D', the quantity of the fluid issuing in the given time will be as VD', or VD2=Q

slowly,

slowly, its contents had lost every character of glass, and had completely assumed the stony structure.'

In 1790, Sir James Hall began his experiments; and he

found that he could command the result which had accidentally occurred at the glass house: for, by slow cooling, the bottle-glass was converted into a stony substance; and this again, when melted and rapidly cooled, was restored to its original state of glass;-so that the same substance assumed the stony or the vitreous character, according to the mode of its cooling.

Sir James was afterward induced to make similar experiments on whinstone; (under which name, he includes the substances distinguished in other countries by the terms of basaltes, trapp, wacken, grünstein, and porphyry;) and, after several trials, he completely succeeded with this also: since, according to the mode of cooling, he obtained either glass, or an intermediate substance, the appearance of which he compares to the liver of an animal; and, lastly, by cooling the melted mass very gradually, he obtained a substance differing in all respects from glass, and in texture completely resembling the whinstone.

In order more fully to prove that these effects resulted entirely from the mode of cooling, Sir James made some additional experiments, in which he first reduced the whinstone to solid glass, and, after a second fusion, converted this glass into the stony substance resembling the whinstone. This substance, or artificial whinstone obtained from the glass, he distinguishes by the name of crystallite.

The author then proceeds to give an account of some trials made with seven varieties of whinstone from different places; the results of which confirm what has been already related. We shall therefore pass on to the second part of the paper, which contains experiments on six varieties of lava from Italy and Iceland.

Before he relates these experiments, Sir James makes some observations on lavas in general; and, speaking of sclid lavas, or those which form the interior parts of the currents,

he says:

When these solid lavas are compared with our whinstones, the resemblance between the two classes is not only striking at first sight, but bears the closest examination. They both consist of a stony basis, which frequently contains detached crystals of various substances, such as white felspar and black hornblend. The analogy between the two classes seems to hold through all their varieties; and I am confident that there is not a lava of Mount Etna to which a counterpart may not be produced from the whinstones of Scotland.

This resemblance in external charaeter is accompanied with an agreement no less complete in chemical properties.'

M. Dolomieu and Mr. Kirwan, though they differ widely in many respects, agree in believing, that lavas have never been acted upon by a heat of sufficient intensity to produce complete fusion; and endeavour each, by an hypothesis peculiar to himself, to accourt for their fluidity.'

By quotations from the works of these two gentlemen, it appears that M. Dolomieu believes that the heat of volcanos has but little intensity; and that the fluidity of lavas is produced by a species of dissolution, or by a simple dilation, which permits the parts to glide over each other; or perhaps by the help of some other matter, which serves as the vehicle of fluidity.-Mr. Kirwan, however, adopts only the latter opinion; adding that the matter, which promotes fluidity, plainly appears to be no other than sulphur and bitumen.

Sir James Hall then observes that these suppositions are both founded on the belief that, in our fires, nothing but glass can be produced from a lava after complete fusion; which, if taken for granted, would certainly render very difficult the explanation of the phænomena of actual eruptions by means of the known agents of nature: but, continues the ingeniousBaronet, in the subsequent paragraph,

The experiments already described supersede the necessity of supposing any thing different from the common course of nature; for they afford analogically an easy solution of the difficulty, by shewing that glass is not the only result of fusion, and that whin, a substance like lava, when cooled slowly after fusion, resumes its stony character."

In order, however, to ascertain the truth of these conclusions, some experiments on lavas were performed of which we regret that the particulars cannot here be stated; and that we can only observe, in general, that the results perfectly correspond with those which were afforded by the whinstones. The crystallites obtained from whinstone and lava were frequently less fusible than the original substances; and Sir James observes that, when the melted glasses were crystallized in the temperature of 22 of Wedgwood's pyrometer, they crystallized rapidly, and formed what he calls the liver crystallite infusible under 30: but, when crystallized in a higher temperature, they formed a stony substance like a common lava, or whin, fusible only at 35.

The paper concludes with some remarks on the formation of lavas, and of the substances contained in them; after which, we find a table shewing the relative fusibilities of the original substances employed in the above experiments, as well as those of the different glasses and crystallites obtained from them.

We

We need not here enter into any discussion of Dr. Hutton's Theory: but, independently of this or of any other system, it must be evident that Sir James Hall's experiments are truly valuable and important; since they reveal the hitherto occult cause which produces the stony character of lavas, and present to chemists and naturalists a series of new and curious facts relative to the fusion of earthy substances.

A Chemical Analysis of three Species of Whinstone, and two of Lava. By Robert Kennedy, M. D. F. R.S. & F. A. S. Edin burgh. The whinstones and lavas examined by Dr. Kennedy were part of those which Sir James Hall, assisted by Dr. K., subjected to the experiments that have been just noticed. In the beginning of this paper, we find the author's general mode of analysis exemplified by a description of the analysis of the basalt of Staffa: but, as this does not appear to be essentially different from that which is usually adopted by modern chemists, we shall omit the particulars. By his analysis, Dr. K. obtained from too parts of the basalt of Staffa,

The loss, therefore, amounted to 6 per cent.; and Dr. Kennedy, having remarked nearly the same loss in other similar analyses which he had formerly made, began to suspect that some saline substance existed in these stones; which suspicion was corroborated by their considerable fusibility. By some subsequent experiments, he ascertained the presence of soda; and he describes the method employed to obtain the soda, and to determine its quantity.

Dr. K. first tried the effects of sulphuric acid in a boiling heat but, although this experiment was continued in one instance even so long as 18 hours, he found that not more than two or three parts of soda could thus be separated.

It appeared necessary, therefore, (he observes) to try other methods; and after some consideration it occurred to me, that if the powdered whins could be exposed, while red hot, to the vapours of the sulphuric acid, also in a red hat state, its power in separating the whole of the alkali from the earthy bases of these substances, would probably be greatly increased in so high a temperature. I succeeded in applying a red heat both to the powdered stone, and to the acid at the same time, by the following means;

‹ Some

Some of the basalt of Staffa being mixed, in very fine powder, with three parts of sulphuric acid, the mixture was evaporated slowly to dryness in a sand bath. The dry mass was then heated gradually to redness, and kept in the fire for one hour. It was next powdered, and boiled in water; and the water, being filtered, was treated with carbonate of ammonia, which threw down a small quantity of a brownish precipitate. After separating this precipitate by filtration, the liquor was evaporated to dryness, and the sulphate of soda, which was left, was purified in the manner already described, and heated red hot. It amounted to 9 parts for every 100 parts of the basalt employed.

In this experiment, the sulphuric acid was first united to a part of the lime, of the argil, and of the iron, contained in the stone; and afterwards, when the mass was exposed to a red heat, the acid was driven off partly or wholly from these, and applied in red hot vapours to every part of the powder; by which its action appears to have been rendered much more powerful, as 9 per cent. of sulphate of soda was produced and by the same process, so simple and easy to execute, I got from the rest of the substances, to be mentioned in this paper, from 8 to 11 per cent. of sulphate of soda, although, when they were merely boiled in the acid, the quantity of this salt never exceeded 5 or 6 per cent.

As the proportion of acid and alkali in neutral salts has not been hitherto determined with certainty, the quantity of soda in these whins cannot be exactly known. But it is probable that 9 parts of sulphate of soda, dried by a red heat, do not contain less than 3 or 4 parts of pure alkali; which must therefore be considered as the weight in 100 parts of the basalt of Staffa: and as 3 or 4 parts of soda, when added to the sum of the earths and iron, amount nearly to the 100 parts of the stone employed in the analysis, this calculation may be reckoned very near the truth. For the same reasons I think it likely, that the greater part, or the whole of the soda, was obtained from the basalt by the process which has been last described.'

Dr. K. remarked, in the course of his experiments, some traces of muriatic acid; the quantity of which he therefore ascertained in the usual way, by means of nitrate of silver.

According to the results of the different processes, it appears that the three species of whin and the two lavas are thus composed:

1. Basalt of Staffa.