concentric rings, which constantly possessed the same order. The external ring was darkish yellow, to which succeeded a deep red beneath a purple; and the third was a deep azure, which passed into a clear sky-blue; then returned the yellow, followed by the purple and the azure, and so on. These rings may be seen by the naked eye, but are best viewed by a lens. The number of series is not constant, being three or four, up to seven. They are always round a dark pulverulent central spot, which is an oxide of silver. All attempts to produce these rings on platinum failed.

Sig. Fusinieri remarks, after some other observations, that the colours farthest from the spot heated, are those first formed, and the nearest the last formed. Hence, the order in which they should be considered is from the external ring inwards. The first coloured zone is the largest, and it is larger as it is farther from the heated spot. The coloured rings, also observed by Newton between object glasses, and on soap-bubbles, vary in size; but with this difference, that they are always smaller as they recede from the centre, whilst the metallic tints are larger in the same situation.

If, in similar circumstances, a greater number of series be obtained, the zones are always narrower; and when the number is few, they are larger.

When there is a succession of series, the first is composed of dark yellow, dark red, dull purple, and dark azure, which passes into sky-blue. The colours of this first series become obscured by time, an effect not remarked as yet in the colours of the other series. The green is wanting in it.

The second series commences with yellow, then a fine purple, a bright azure, and a fine green.

The third series is composed of yellow, purple, bright azure, very narrow, and scarcely discernible, and then a dull green. This series wants the blue.

The fifth series has only two colours, purple and green, both dull. It entirely wants the yellow.

The sixth series has also only two colours, purple and green, but both dull.

In the first series, where three or four colours may be distinguished, the yellow and purple increase in intensity, from the exterior to the interior; but the blue and the green decrease in intensity, in the same direction. The oxide of the central spot commences immediately upon the edge of the colour of the last series.

Deductions.-These results shew the strong analogy between the systems of colours produced by heat on metals in contact with the air, and those reflected by thin plates described by Newton. This point admits of farther research, and it is probable the size of the coloured zones or metals will follow the same law of decrement found to obtain with the coloured rings produced by object glasses.

This analogy induces the supposition that, in the combination of oxygen with the surface of the heated plate of metal, a thin pellucid coat of oxide is formed, diminishing in thickness as it recedes from the centre of the heat, as indicated, indeed, by the distribution of the observed colours. This idea leaves nothing mysterious in the appearance of these phenomena, except that belonging to these plates generally, and their manner of producing these particular effects. On this point nothing better than the hypothesis of Newton has, since his time been advanced.

The action of heat is not sufficient to produce these phenomena; the access of oxygen, which may combine with the metal chemically, is required. This may give rise to the query, whether oxygen has not a general influence in the production of such effects. It has certainly been proved that, when a reflection of these colours, in this order, is obtained, that reflection is occasioned by thin plates; but the inverse of this proposition, namely, that whenever thin plates are formed, these colours, in this order, are reflected, has not been proved; and there are, indeed, even arguments to support the contrary; as, for instance, the bubbles of various solutions, which, though very thin and lasting, do not give any appearance of colour.

Giornale di Fisica, II. p. 145.

2. Analysis of Mixtures of the Chlorides of Potassium and Sodium.-This process is founded on the unequal diminution of temperature which these chlorides produce by their solution in water; 50 grammes, (772.2 gr.) of chloride of potassium, when dissolved in 200 grammes (3088.8 gr.) of water, contained in a glass vessel of the capacity of 320 grammes (4942 gr.) of water, and of the weight of 185 grammes (2875.1 gr.,) produce a diminution of 11°.4 centigrade (20.52 Fahrenheit.) The same quantity of chloride of sodium gives, in the same circumstances, a depression of 10.9, (3.42 Fahrenheit.)

Now, if a mixture of the two chlorides be made, and 50 grammes (772.2 gr.) be dissolved in 200 grammes (3,088.8 gr.) of water, the cold produced will be proportional to the quantities of each of the chlorides; and it is always possible to deduce the one from the other. A table may be made, indicating the diminution of temperature corresponding to known mixtures of the two clorides, but it is sufficient to calculate their proportion by a simple rule of alligation, taking the diminution of temperature produced by the solution of each chloride in water. Making d this diminution, the rule by which to calculate the chloride of potassium in 100 parts of a mixture, with the degree of cold given, is

Chloride of potassium 100-190

9.5

In operating on known mixtures, the proportions calculated by this rule do not differ from the true proportions by more than one-hundredth. The only precautions required for this precision are, 1st, to have a very sensible thermometer, on which the tenths of degrees may be read with ease: 2d, to reduce the mixture to a fine powder, that it may dissolve as rapidly as possible in the water: 3d., to hold the vessel by the neck, only so that the heat of the hand may not influence the temperature of the water. The manner of operating is as follows:

be

Having weighed 200 grammes (3088.8 grs.) of water into the glass vase, in which the solution is to be made, the thermometer is to be introduced to ascertain its temperature, which may supposed 20°.4 (68.72 Fahrenheit;) 50 grammes (772.2 gr.) of the mixture are then quickly introduced, and whilst the

thermometer is suspended in the liquid by the left hand, the vessel is to be held by its neck in the right, and a rapid whirling motion given to it, to accelerate the solution. Whilst this is doing, the thermometer falls rapidly; it is to be observed with attention, and the lowest degree to which it passes noted. Suppose this 120.8 (58.04 Fahrenheit.) The diminution of temperature d is consequently 20°.4 - 120.8 70.6 (13.68 Fahrenheit,) and the chloride of potassium is equal to 100×7.6—190 = 60.

9.5

This process, which scarcely requires ten minutes to be completed, is susceptible of the greatest precision, and, in consequence of its simplicity, may readily be employed in the arts. It is especially advantageous in the preparation of nitre, for the analysis of the salts which are deposited during the evaporation of the water, and which are the chlorides of potassium and sodium, in very variable proportions.

Nitre produces also much cold by its solution in water. The means which have been noticed are also applicable to the analysis of a mixture of nitre and common salt. In general, this method may serve for all those bodies which produce very unequal diminutions of temperature by solution in water, or in any other liquid.-Annales de Chimie., XII., p. 42.

3. Discovery of pyroligneous Acid.

MR. EDITOR, Sir,-In the Revue Encyclopédique, M. le Comte Chaptal has published an article de l'Industrie Françoise, in which, among other things, pyroligneous acid is enumerated as being one of the discoveries made in the arts by the French. Whenever priority of discovery is wrongfully claimed, it may be well to point it out, that the merit of originality may be attached to its proper claimant. With this view, I have copied the following statement from a work printed by Cooke, London, in the year 1661, entitled, the Sceptical Chemist, in which it appears, that pyroligneous acid is of much earlier origin than is commonly supposed, and that the fact of its forming sugar of lead with minium was known one hundred and fifty-eight years ago.

Page 194.

"that the sour spirit of box not only would,

as I just now related, dissolve corals, which the other* would not fasten on, but being poured upon salt of tartar, would immediately boil and hiss, whereas the other would lie quietly upon it. The acid spirit poured upon minium made a sugar of lead, which I did not find the other to do."

--

Page 195. I found, according to my expectation, that the acid spirit had really dissolved the corals, and had coagulated with them. For, by the affusion of fair water, I obtained a solution which (to note that singularity upon the bye) was red; whence the water, being evaporated, there remained a soluble substance, much like the ordinary salt of coral, as chymists are pleased to call that magistery of corals, which they make by dissolving them in common spirit of vinager.” And, in page 192, the " soure spirit" obtained from the distillation of box is expressly called "vinager."

By inserting the above account in the Journal of Science, you will oblige, Sir, your humble servant,

Bristol, 16th Nov. 1819.

E. T. J.

4. Preparation of Nitric Ether, by M. Bouillon Lagrange.After having made a mixture of equal parts of nitric acid at 36° (S.G. 1.333) and alcohol, at 40° (S.G. .817), it is to be introduced into a matrass.

Then copper turnings are to be put into a flask, to which an S tube is to be connected, by which nitric acid may be poured on them, and another tube also to convey the nitrous gas into the mixture of acid and alcohol. A Woolfe's apparatus is to be connected with this flask, the bottles being half filled with a solution of muriate of soda, and placed in a cooling mixture. The joints being luted, I pour nitric acid in small portions on the copper turnings. The gas disengaged is absorbed. only in part by the alcohol, and part passes into the vessels at the extremity of the apparatus. The mixture heats gradually, and, at the end of an hour and a half, it begins to boil. The

*The aqueous and oily part procured by distillation, after saturating the acid with coral.