same tests showed that a much smaller quantity of muriatic acid was carried over than in the former experiments.

When water was distilled in a similar way over muriate of lime, the distilled water became considerably turbid with nitrate of lead; in the common temperature of the atmosphere, neither oxalate of ammonia, carbonate of ammonia, carbonate of soda, nor nitrate of silver, produced turbidness; but when the water was boiling hot, both oxalate of ammonia and nitrate of silver occasioned turbidness. When five grains of carbonate of soda were dissolved in five ounces of the distilled water and evaporated to half an ounce, no precipitate was observed. Litmus paper was not at all affected by the distilled water.

Water distilled over muriate of barytes was rendered very turbid by a solution of nitrate of lead; a solution of nitrate of silver produced only a turbidness when added to the boiling-hot water. Neither carbonate nor sulphate of soda rendered the water turbid, but when it was boiled with sulphate of soda, turbidness appeared on cooling. Litmus paper was not affected by the water.

In water distilled over muriate of ammonia, both nitrate of lead and of silver immediately occasioned turbidness and precipitation. The same effect took place after the distilled water had again been subjected to distillation. Three ounces of the distilled water when mixed with three drops of a concentrated solution of nitromuriate of platina, and evaporated until only five drops remained, left a reddish yellow precipitate, which was difficultly soluble in water. Litmus paper was not affected.

*

Although nitrate of lead might not in all these experiments be a test of muriatic acid, for which it seems M. Kruger had used it, yet nitrate of silver was, with few exceptions, acted upon as if muriatic acid had been present. Any doubts which might remain as to the accuracy of the result have been removed by M. Vogel, who boiled an ounce of completely neutral muriate of magnesia in 12 ounces of distilled water with sufficient precautions to prevent any of the salt from being carried over mechanically. The vapours were made to pass through a very dilute solution of nitrate of silver, and rendered it turbid in a quarter of an hour. One part of the solution was kept in a glass covered with black paper, and did not assume any colour; the other was exposed to the rays of the sun, and became red in a few minutes. In another experiment, the vapours passed through tincture of litmus, which they did not redden, but made the colour rather darker.

The same result was obtained when a solution of pure muriate of soda was distilled, and sea-water from the Mediterranean which had been kept in a laboratory for nine years, produced similar effects. The precipitate, which in these different expes

Gilbert's Annalen, 1822, No. 11.

riments was obtained, had all the properties of muriate of silver.

An opinion had been entertained that the property of precipitating nitrate of silver might depend upon the presence of sulphuretted or phosphuretted hydrogen. To refute this opinion, M. Vogel boiled down eight ounces of sea-water to two ounces; then added six ounces of distilled water, and evaporated until only two ounces were left; added again six ounces of distilled water, distilled again; and repeated in this way the experiment four times constantly with the same effect upon a solution of nitrate of silver. According to the experiments of M. Vogel, every kind of water he could get in the kingdom of Bavaria, either procured from rivers, springs, or brooks, contained so much of a muriate that it gave a precipitate with a solution of nitrate of silver. M. Vogel draws from these experiments the conclusion, that the muriates to a certain degree are volatilized by steam, and that they exist in the state of neutral salts in the distilled water. The same experiments were afterwards repeated by M. Bertram, who found that water when distilled with sufficient care over muriate of lime, did not carry over any of the component parts of that salt, for neither oxalate of potash, nor nitrate of silver, produced any turbidness in the distilled water. But when a solution of muriate of magnesia was distilled in a similar way, a considerable quantity of free acid passed over, and principally towards the end of the distillation when the solution became more concentrated. Prof. Pfaff* also repeated the experiments on boiling sea-water with sufficient care, and allowed the vapour to pass through a solution of nitrate of silver. He discovered a double action, the partial formation of muriate of silver, and the deoxidation of a part of the oxide of silver by means of pure steam. The result of his interesting experiments is this: when the vapour of pure distilled water is made to pass through a solution of nitrate of silver, this solution assumes all the different shades between yellow and dark-brown, according to the concentration of the solution, and the length of time in which the steam has passed through it. The colour is not very observable before the solution of the nitrate of silver has acquired the temperature of boiling water; but when it has reached it, the colour increases rapidly. If several glasses are connected by tubes, and all successively raised by the steam passing through them to the boiling temperature, all assume the colour. Nitric acid destroys the colour of this solution of nitrate of silver; and while the steam is producing this effect upon the solution, oxygen is disengaged. When steam, in a similar way, is passed through a solution of gold, a beautiful blue liquid is produced like that which is obtained by adding oxalic acid to a solution of gold.

It seems thus to be proved pretty clearly that the steam acts

Schweigger's Journal, 1822, ix.

in these cases by deoxidizing the salts of silver and gold. Neither muriate of platina, nor protonitrate or pernitrate of mercury, were acted upon by steam in a similar manner.

The observations of the Dutch chemists, which are scattered in a number of different dissertations, have been collected and again published by Dr. Driessen,* and they possess great interest. Prof. Driessen, of Groningen, made the first experiments in July, 1800, at Amsterdam, where he poured several ounces of pure water 500 times through a glass funnel from one vessel into the other. The water sometimes exhibited a slight trace of sulphuretted hydrogen, but it constantly threw down nitrate of silver, of a white colour. These experiments were made at different hours of the day, and in different heights above the ground, but constantly with the same result, if it had not rained for a considerable time. When, however, M. Craanen, who had been present at these first experiments, tried them again after rainy weather, he did not obtain any precipitate at all. In Groningen, he did not find any muriatic acid in the air, except once in 1802, when, after a long dry season, a thick fog came on; water which had been poured in the way above-mentioned, occasioned a precipitate în nitrate of silver, and reddened even tincture of litmus. Dr. Von Rossem could not afterwards detect any trace of muriatic acid.

The fact that the air near the sea-shore contained free muriatic acid was applied to explain the frequency of that dreadful disease the colica saturnina, at Amsterdam, where it had been observed oftener than in any other town. It was conceived that the free muriatic acid dissolved the lead from the roofs of houses, and communicated it to the rain water.

A new series of experiments was, therefore, performed by Dr. Veehof in order to ascertain whether the muriatic acid was really in an uncombined state in the atmosphere; and the results were, that water poured from vessel to vessel at Groningen in the manner already mentioned, and rain-water from the same place, contained no free acid; that water similarly treated near salt springs showed a slight trace of free acid; and lastly, that water at Amsterdam, under the same circumstances, contained a considerable quantity of uncombined acid.

These experiments were twice repeated, and constantly with the same result. They all showed muriatic acid by nitrate of silver, but that from Amsterdam most of it. Besides the water from Amsterdam produced a precipitate when tried with muriate of barytes, and caustic alcali occasioned a more copious precipitate in it than in water, treated in the same way at Groningen.

Prof. Driessen repeated his experiments in 1809 at the Zuider Zee, where, after having poured the water more than 1000 times from one vessel to another; while the direction

* Schweigger's New Journal, b. 6, 2. 1822.

of the wind was such as to carry the breath and perspiration of the surrounding persons away from the water, he found unquestionable traces of free acid; they repeated the experiment again on one of the high dykes near Harlingen with the same result. It was observed that the colour of the litmus paper was particularly affected, when in a dry season the sea was violently agitated. In order to ascertain the cause of this phenomenon, Dr. Von Rossem tried an experiment by exposing a vessel full of fresh sea-water to the rays of the sun, and poured, during that time, water over it; he found in the water distinct traces of muriatic acid.

The experiments of M. Vogel and M. Kruger, which occasioned the experiments about the volatilisation of muriates mentioned before, were the following: In a balloon with two apertures, one above and one below, to make draught, a small vessel containing a solution of nitrate of silver was introduced, and the balloon placed in a covered bathing car, of which one window was open, while the wind generally blew from the land. When, after 21 days, the small vessel was taken out, some bluish-black flakes, and a white powder, were formed. The precipitate, after having been washed, was digested with nitric acid, which dissolved the black flakes, and left a white precipitate, which was muriate of silver.

M. Meisner tried the air at Halle not far from the brine springs, but did not find any muriatic acid.

From all these observations and experiments, the following are the results that the air near the sea-shore (the Baltic, the German Ocean, and the Channel, the latter according to some observations of M. Vogel), contains generally muriatic acid; its quantity is increased by dry seasons, and ceases to exist in rainy weather.

Muriatic acid may be found in the atmosphere at a certain distance from the sea-shore, and it there depends upon similar circumstances as on the coast. It exists mostly combined in' form of neutral muriates, and it is highly probable that by the action of air and atmospheric heat, the earthy and alkaline muriates are not decomposed. In most of the experiments, they passed over at the boiling temperature in the state of neutral salts. Where muriatic acid was most decidedly found in a free state at Amsterdam, it is evident that this at least was partly owing to the sulphuric acid formed by the combustion of coal and peat.

ARTICLE VI.

An improved Method of making Coffee. By J. Smithson, Esq. F. R. S.

SIR,

(To the Editor of the Annals of Philosophy.)

June 4, 1823.

FROM the highly fugacious nature of that part of coffee on which its fine flavour depends, a practice has become very generally adopted of late years of preparing the liquor by mere percolation,

This method has not only the great defect of being excessively wasteful, but the coffee is likewise apt to be cold.

Coction and the preservation of the fragrant matter are, however, not inconsistent. The union of these advantages is attainable by performing the operation in a close vessel. To obviate the production of vapour, by which the vessel would be ruptured, the boiling temperature must be obtained in a water-bath.

In my experiments I made use of a glass phial closed with a cork, at first left loose to allow the exit of the air. Cold water was put to the coffee.

This process is equally applicable to tea.

Perhaps it may also be employed advantageously in the boiling of hops, during which, I understand, that a material portion of their aroma is dissipated; as likewise possibly for making certain medical decoctions.

This way of preparing coffee and tea presents various advantages. It is productive of a very considerable economy, since by allowing of any continuance of the coction without the least injury to the goodness, all the soluble matter may be extracted, and consequently a proportionate less quantity of them becomes required. By allowing the coffee to cool in the closed vessel, it may be filtered through paper, then returned into the closed vessel, and heated again, and thus had of the most perfect clearness without any foreign addition to it, by which coffee is impaired. The liquors may be kept for any length of time at a boiling heat, in private families, coffee-houses, &c. so as to be ready at the very instant called for.

It will likewise prove of no small conveniency to travellers who have neither kettle, nor coffee-pot, nor tea-pot, in places where these articles are not to be procured, as a bottle will supply them.

In all cases means of economy tend to augment and diffuse comforts and happiness. They bring within the reach of the many what wasteful proceedings confine to the few. By