« PreviousContinue »
On the Properties and Nature of the Basis of Potash.
It is difficult to preserve and contine these bodies, as they act upon almost every body with which they come in contact. Recently distilled naphtha answers the best, in it they remain many days unchanged.
The base of potash at the freezing point of water is hard and brittle, and when broken has a beautiful crystalline texture, perfectly wbite, with a high metallic splendour. At 50° Fahrenheit it is soft and malleable. With the lustre of silver ; at 60° and 70° it has an imperfect degree of fluidity; at 100° its fluidity is perfect, and the eye cannot distinguish it from inercury. Ina temperature approaching a red heat, it is cooverted into vapour, and is found unaltered by distillation. It is a perfect conductor of electricity and heat; though in all these sensible properties it resembles the metals, it differs remarkably froin all of them in specific gravity. It does not sink in double distilled waplitha; and Mr. Davy has calculated that its relative weight, compared with water, is as 6 10 10.: This calculation (supposing it not far from the truth), inakes it the lightest fluid body known. It unites with
oxygen in more proportions than If it be heated in a quantity of oxygen pol suffi. cient to convert it wholly into potash, a solid is formed of a greyish colour, which is a mixture of potash, and its basis at a lower degree of oxygenation; this last substance is easily convertible into potash, by an additional quantity of oxygen. In oxyın uriatic acid, the bases of potash inflames spontaneously, and forins muriate of potash. It decomposes water with great violence, hydrogen escapes, there is an explosion with a brilliant fiame, and a solution of pure potash is the result. So great is the energy of its action upon water, that it discovers and decomposes the small quantities of water contained in alcohol and ether, even when they have been carefully puritied, Its action upon the sulphuric arid nitric acids is such as may be expected from its superior altraction to oxygen.
It forins alloys with metals, and sulphurets and phosphorets with sulphur and phosphorus; it unites withi mercury in several different proportions ; one part added to 9 or 10 of mercury (in volume) formas a substance exactly like mercury in colour, but the parts of which seem to have less coherence; if a globule be brought in contact with a globule of mercury of twice its size, they unite with considerable heat ; at the temperaluie of ils combination, the compound is fluid, but when
çool it appears as a solid inetal of the colour of silver. By adding more of the basis of potash, so as to be about noth of the weight of the mercury, the amalgam increases in hardness and beconies brittle. Exposure to the air destroys these combinations, the basis by attracting oxygen becomes potaslı, which deliquesces; and the mercury is separated unaltered. Water" likewise effects the same decomposition ; gold, silver, or copper are also dissolved by this substance, and these alloys are likewise decomposed by water with the same circumstances as the amalgam of inercury. From the oils, both concrete and volatile, the basis of potash precipitates charcoal, some gas is liberated, and a soap is formed; camphor exhibits the same phenomena, except that no gas is liberaled. These experiments furnish an easy and elegant proof of the existence of oxygen in oils. Metallic oxides, as of iron, lead, and tin, are received by it. In consequence of this property, it decomposes flint glass and green glass by a gentle heat: alkali being formed by the oxygen from the oxides, which dissolves the glass. But even the purest glass is aliered at a red heat; the alkali of the glass, and the basis of potash uniting into a deep red brown substance, which is the raw substance at its lower degree of oxygenation.
On the Properties and Nature of the Busis of Soda. All the experiments from which Mr. Davy obtained the results we have collected in the preceding paragraph, were repeated with the basis of soda, and they are enumerated in the lecture in a similar order. But the general properties are so analogous (as might be expected) to those of the basis of potash, that we think it needless to do more than mention iis peculiarities. - It is white, opaque, with the lustre and appearance of silver, exceedingly malleable, and much softer than any common sub. stance; it may by pressure be spread into thin leaves; and the property of welding, which belongs to iron and platina at a white heat only, is possessed by this substance at common temperatures; its specific gravity was found by an ingenious process to be 95.3, water being 1. It loses its cohesion at 180° Fahrenheit, and fuses perfectly at about 180°. Al what degree it is volatile has not been ascertained.
We do not think it necessary to relate at length the experiments which Mr. Davy has made to determine the proportion of oxygen to the basis, which enters into the composition of the fixed alkalies. The quantities operated upon were so minute, that tbough we doubt not that
every thing has been effected which could be done by the most happy manipulation, we can hardly put entire confidence in the results. To arrive at bis conclusions Mr. Davy used both combustion in oxygen gas, and the decomposition of water ; in the last case, measuring the hydrogen which is let loose, gives, by an easy calculation, the oxygen which is absorbed. The last method the author has found subject to the least uncertainty, from accidental .variations, and it is probably most to be depended upon. Upon the whole Mr. Davy thinks him self authorized to conclude, that potash is composed of about 6 parts basis, and I of oxygen : and that soda consists of 7 parts basis, and 2 of oxygen.
Mr. Davy concludes this part of his lectures with the inquiry, whether these newly discovered substances should be termed metals. They agree, he observes, with metals in opacity, lustre, malleability, conducting power as to heat and electricity, and he adds, a little precipitately we think, in their qualities of chemical combination. We say precipitately, for surely it will not be said, that their combinations with acids, are similar to metallic salis, or with oxygen are like metallic oxides. But if they must be arranged under some of the present genera of natural bodies, the metals are those which they most resemble, and Mr, Davy's names for them, potassiumn and sodium are perhaps the least" objectionable that could be des vised. We are inclined to suspect, that the discovery of the first step towards these bodies will be proving the com. pound nature of the common metals.
The bases of the fixed alkalies being detected, a suspicion would naturally arise that ammonia, which has been thought to be composed of hydrogen and nitrogen, might really be an oxide. A small quantity of oxygen might have escaped the observation of former chemists, who have analysed this alkali, passing off under the form of water. Several observations have convinced Mr. Davy that ammonia contains a small proportion of oxygen. · The most conclusive experiment is the decomposition of ammonia by electricity, first performed by M. Berthollet. As there were some incongruities in the results, as corded by Berthollet, and a want of coincidence between thein and those of other experimenters, Mr. Davy bas repeated the process with every precaution to avoid the circumstances which miglit bave occasioned error.
Sixty measures of ammoniacal gas, each equal to a grain of water, were electrized, till no farther expansion could
be produced, the gas filled a space egual to that occypied by 108 grains of water. Platina wires were used io conduct the electricity. The 108. measures of gas carefully analyzed, were found to consist of 80 measures in volume of hydrogen, and 28 measures of nitrogen. Two experiments of Messrs, Allen and Pepys on the weight of ammoniacal gas, gave the following result: “In the first experiment 2,1 cubic inches of ammonia weighed 4.05 grains; in a second experiment the same quantity weighed 4.06 grains, barometer 30.65, thermometer 54 Fahrenheit." From these data the 60 cubic inches of ammonia weigh 11.2 grains. The 80 of hydrogene gas weigh 1.93 grains, the 28 of nitrogene 8.3. Sum, 10.2. There remains therefore one grain of ammoniacal gas more than the products of hydrogen and nitrogen, which is nearly itth of the whole employed ; and this loss Mr. Davy concludes, “ can only be ascribed to the existence of oxygen in the alkali, part of which probably combined with the platina wires employed for electrization, and part with hydrogen."
This hypothesis will explain the phenomena of the production and decomposition of ammonia as well as that which is commonly received. Ammonia is formed in cases where these three elements are always present, and during the decomposition of bodies in which oxygen is loosely attached. When it is decomposed at the heat of ignition, the affinity of hydrogen for oxygen prevails over the complex attraction of the three elements, water is formed, and hydrogen and nitrogen are cooled. It would seem then that the principle of acidity in the French nomenclature might likewise be called the princi, ple of alkalescence.
Mr. Davy has tried some experiments upon barytes and strontites, with a battery of very high power, which go far to prove that these earths have likewise combustible bases united to oxygen. There was a vivid action and a brilliant light at both points of communication, and an inflammation at the negative point, but he has not yet succeeded in collecting the substance which is produced.
Besides the direct importance of the discovery of these metals (if they should be so called) it cannot be doubted that they will prove most powerful agents in the ana. lysis of other bodies. As an example of its power, we inay mention that it oxidates in carbonic acid, decomposes it, and produces charcoal when heated in contact with carbonate of lime.' It likewise oxidates in muriatic acid, but Mr. Davy 'has not hitherto ascertained the result of this decomposition.
We believe we need not apologize to our readers for _having been so copious in our account of this lecture. The facts contained in it are perhaps the most important of any which the industry of modern chemistry has brought to light; they open new views in all the sciences connected with analytical researches, and will assuredly confer immortality upon the indefatigable, acute, and modest philosopher, to whom we owe their developement. II. On the Structure and Use of the Spleen. By Everard
Home, Esq. ¥.R.S.
Mr. Home's opinion of the use of the spleen is that its vessels probably have a 'power of absorbing liquid matter immediately from the cardiac portion of the stomach, and conveying it to the blood.' By this function he conceives the liquid matter which is not necessary to digestion, is prevented from mixing with the digested food, which passes from the pylorus. The experiinents by which he has at lempied to establish this theory are convincing enough, if the experimenter has not been biassed by a pre-conceived opinion ; for we inust remark, that Mr. H. formed his theory first, and afterwards set about to prove it; this we do not think the very best road to the truth. Tincture or infusion of rhubarb was given to animals, (chiefly to asses); after a time the animal was killed, and by the aid of an alkaline test, it was discovered that the rhubarb was abundant in the spleen, and in the serum of blood drawn from the splenic vein, when it could not be delected elsewhere. Ti is also asserted, that after an apinal has taken in liquid, the spleen is turgescent, and it contracts as it becomes unloaded.
Mr. Home believes that he has discovered the spleen to be of a cellular structure,
When the spleen is turgid with fluid, the cells, he says, are visible to the baked eye, but when it is empty they cannot be observed. This account is in substance the same as Malpighi's, who has described it as consisting of small hollow glands. A cell and a small hollow gland are we think synonimous.
Doubtless, if these facts are confirmed, they are of consderable importance, and will throw light on a very obscure point of physiology, and we think that Mr. Home deserves much credit for having led the way in the investigation