I have lately employed as an eudiometrical substance the solution of green muriate, or sulphate, of iron, impregnated with nitrous gas; and I have found that it is in some respects superior to many of the bodies heretofore used, as it rapidly condenses oxygen without acting upon nitrogen; and requires for its application only a very simple and a very portable apparatus.

As

This fluid is made by transmitting nitrous gas through green muriate, or sulphate, of iron, dissolved to saturation in water.* the gas is absorbed, the solution becomes of a deep olive brown, and when the impregnation is completed it appears opaque and almost black. The process is apparently owing to a simple elective attraction; in no case is the gas decomposed; and under the exhausted receiver it assumes its elastic form, leaving the fluid with which it was combined unaltered in its properties.

The instruments necessary for ascertaining the composition of the atmosphere, by means of impregnated solutions, consist simply of a small graduated tube, having its capacity divided into one hundred parts, and greatest at the open end; and of a vessel for containing the fluid.

The tube, after being filled with the air to be examined, is introduced into the solution; and, that the action may be more rapid, gently moved from a perpendicular towards a horizontal position. Under these circumstances the air is rapidly diminished; and, in consequence of the dark colour of the fluid, it is easy to discover the quantity of absorption. In a few minutes the experiment is completed, and the whole of the oxygen condensed by the nitrous gas in the solution in the form of nitrous acid.

In all eudiometrical processes with impregnated solutions, the period at which the diminution is at a stand must be accurately observed; for, shortly after this period, the volume of the residual gas begins to be a little increased, and, after some hours, it will often fill a space greater by several of the hundred parts on the scale of the tube, than that which is occupied at the maximum of absorption.

This circumstance depends upon the slow decomposition of the nitrous acid (formed during the experiment), by the green oxide of iron, and the consequent production of a small quantity of aëriform fluid (chiefly nitrous gas); which, having no affinity for the red muriate, or sulphate, of iron produced, is gradually evolved, and mingled with the residual nitrogen.

The impregnated solution with green muriate is more rapid in its operations than the solution with green sulphate. In cases when these salts cannot be obtained in a state of absolute purity, the com

• Dr. Priestley first observed this process: for a particular account of it, see Researches, Chemical and Philosophical, page 152. Johnson.

The decomposition of nitrous acid, by solutions containing oxide of iron, at its minimum of oxidation, is a very complex process. The green oxide, during its conversion into red oxide, not only decomposes the acid, but likewise acts upon the water of the solution; and ammoniac is sometimes formed, and small portions of nitrous oxide and nitrogen evolved with the nitrous gas.

mon or mixed sulphate of iron may be employed. One cubic inch of moderately strong impregnated solution is capable of absorbing five or six cubic inches of oxygen, in common processes; but the same quantity must never be employed for more than one experi

ment.

A number of comparative experiments, made on the constitution of the atmosphere at the Hotwells, Bristol, in July, August, and September, 1800, with phosphorus, sulphurets of alkalies, and impregnated solution, demonstrated the accuracy of the processes in which the last substance was properly employed. The diminutions given by the sulphurets were indeed always greater by a minute quantity than those produced by phosphorus and impregnated solutions but the reason of this will be obvious to those who have studied the subject of Eudiometry. In no instance was it found that one hundred parts in volume of air contained more than twenty one of oxygen and the variations connected with different winds, and different states of temperature, moisture, &c. were too small, and too often related to accidental circumstances, to be accurately noticed.

In analysing the atmosphere in different places, by means of impregnated solutions, I have never been able to ascertain any notable difference in the proportions of its constituent parts. Air, collected on the sea, at the mouth of the Severn, on October 3rd, 1800, which must have passed over much of the Atlantic, as the wind was blowing strong from the west, was found to contain twenty-one per cent. of oxygen in volume; and this was nearly the proportion in in air sent from the coast of Guinea, to Dr. Beddoes, by two Surgeons of Liverpool.

If we compare these results, with the results gained more than twenty years ago, by Mr. Cavendish, from experiments on the composition of atmospherical air, made at London and Kensington; considering, at the same time, the researches of Berthollet in Egypt and at Paris, and those of Marti in Spain, we shall find strong reasons for concluding, that the atmosphere, in all places exposed to the influence of the winds, contains very nearly the same proportions of oxygen and nitrogen, a circumstance of great importance; for, by teaching us that the different degrees of salubrity of air do not depend upon differences in the quantities of its principal constituent parts, it ought to induce us to institute researches concerning the different substances capable of being dissolved or suspended in air, which are noxious to the human constitution: particularly as an accurate knowledge of their nature and properties would probably enable us, in a great measure, to guard against, or destroy, their baneful effects.

Outlines of Observations relating to Nitrous Oxide, or Dephlogisticated Nitrous Air. By MR. DAVY, Director of the Chemical Laboratory, and Lecturer on Chemistry in the Royal Institution.

ARTICLE I.

Sect. 1. The aëriform fluid that constitutes the subject of the following observations, was called by its discoverer, Dr. Priestley, dephlogisticated nitrous air. The Dutch chemists, who, some time ago, investigated certain of its properties, named it gaseous oxide of azote. Lately, in this country, it has been denominated nitrous oxide, which, according to the principles of the French Nomenclature, signifies nitrogen in the first degree of oxygenation. This term cannot well be confounded with nitrous gas; and it bears the necessary analogy to words denoting other combinations of oxygen and nitrogen.

Sect. 2. A short and general account of the production and properties of nitrous oxide will not, perhaps, be wholly unacceptable to the chemical world; particularly as the most remarkable agencies of this substance are but little known out of Great Britain; and they are connected with curious philosophical enquiries.

II. On the Production of Nitrous Oxide.

Sect. 1. As yet nitrous oxide has not been composed immediately from its elements; and there is no reason to believe that it is produced in any of the operations of nature. But it may be procured in a number of artificial processes, during the decomposition of nitrous gas and nitric acid.

Sect. 2. Nitrous gas may be converted into nitrous oxide in two modes. First, by the simple abstraction of a portion of its oxygen by bodies possessing a strong affinity for that principle, such as alkaline sulphites, muriate of tin, and sulphurets. Secondly, by the combination of a body with portions both of its oxygen and nitrogen, such as hydrogen, when in a peculiar state of combination, or in a nascent form.

a. The alkaline sulphites convert nitrous gas into nitrous oxide with much greater rapidity than any other substances.

At temperature 46°, Fahrenheit, sixteen cubic inches of nitrous gas were converted in less than an hour into 7-8 cubic inches of nitrous oxide, by one hundred grains of pulverised sulphite of potash containing its water of crystallization. During this process, the sulphite became partially converted into sulphate; but no sensible increase of temperature was produced. No water was decomposed, nor was any free nitrogen evolved.

Muriate of tin, and the sulphurets,† whether solid or in aqueous

⚫ Nitrous gas, according to the strict principles of the French Nomenclature, ought to be called nitric oxide.

Dr. Priestley first noticed the conversion of nitrous gas into nitrous oxide by sulphurets. To the Dutch chemists we owe the discovery of the action of muriate of tin on nitrous gas

solution, act slowly upon nitrous gas, and became oxygenated, whilst they convert it into nitrous oxide. The diminution of the nitrous gas, in these processes, is the same as in the process with sulphite of potash.

b. When nitrous gas and sulphurated hydrogen gas are mingled together, they slowly decompose each other, with great diminution of volume. In this operation, nitrous oxide is formed,* sulphur is deposited, and signs of the production of ammoniac and water are perceived. There is every other reason to believe that the hydrogen of the sulphurated hydrogen is the great agent in effecting this decomposition, by combinining with portions of both the oxygen and nitrogen of the nitrous gas, to produce water and ammoniac. For no perceptible quantity of acid is formed in the experiment; and the sulphur deposited appears to be in its common state. This opinion indeed is further proved, by the phenomena connected with the decomposition of nitrous gas by nascent hydrogen.

When nitrous gas is exposed to nascent hydrogen, whether it be procured by the action of metals upon water, in common cases, or in Galvanic experiments, ammoniae and nitrous oxide are uniformly produced; and the volume of the nitrous gas diminishes nearly to the same extent, as in the process with sulphurated hydrogen, i. e. to about one-third.

Sect. 3. Nitrous oxide may be procured from nitric acid, when this substance is decomposed by certain metallic bodies; and likewise during the mutual decomposition of nitric acid and ammoniac at certain temperatures.

a. During the action of zinc, iron, or tin, upon diluted nitric acid, certain quantites of nitrous oxide are produced, but mingled with nitrous gas and nitrogen. In these processes, as has been long known, ammoniac is formed; and consequently water is decomposed: a circumstance most probably connected with the production of the nitrous oxide; for the quantity of the gas is less in proportion as the acid is more concentrated.

b. Nitrous oxide, perfectly pure, may be obtained in an easy manner, and at a cheap rate, from the decomposition of nitrate of ammoniac. This salt, when deprived of as much of its water of crystallization as possible, becomes fluid at the temperature of 320°, Fahrenheit, and immediately begins to be converted into water and nitrous oxide.+

One hundred grains of salt, perfectly decomposed at any temperature between 320° and 620°, produces about 57 grains of gas, and 43 of fluid. In experiments on this decomposition the heat must be carefully applied and regulated; as at temperatures above 800°, nitrate of ammoniac detonates, and becomes changed into nitrous gas, nitric acid, water, and nitrogen.

Mr. Kirwan first observed the peculiar action of sulphurated hydrogen on nitrous gas.

+ To Mr. Berthollet we owe the discovery of the products evolved during the slow decomposition of nitrate of ammoniac.

III.-On the Combinations of Nitrous Oxide.

Sect. 1. Pure water is capable of holding in solution, at the common temperatures of the atmosphere, a quantity of nitrous oxide equal to about half its volume.* Water impregnated with nitrous oxide, has a sweetish taste, which is hardly perceptible, except to delicate organs: and it becomes effervescent on agitation. It is possessed of no action in vegetable colours; and effects no perceptible change in metallic solutions.

Nitrous oxide is expelled unaltered from water at temperatures equal to about 212°. It is likewise incapable of remaining in combination with it, when the pressure of the atmosphere is removed.

Nitrous oxide is expelled from water by muriatic acid, carbonic acid, and sulphurated hydrogen; but it has a stronger affinity for that fluid than nitrous gas, oxygen, or hydrogen.

Sect. 2. Ether, alcohol, and the volatile and fixed oils, dissolve nitrous oxide in larger quantities than water at common temperatures; but without undergoing any material alteration in their properties. The gas is incapable of remaining in combination with them at the temperature of their ebullition, or under the exhausted receiver.

Sect. 3. Nitrous oxide has as yet been combined with no solid bodies, except the fixed alkalies; and even the affinities of water, alcohol, ether, &c., for this gas appear to be diminished when they hold in solution neutral salts and other substances. The sulphurets, the sulphites, and the different bodies that act upon nitrous gas, both dry and in solution, effect no alteration in the composition of nitrous oxide.

Sect. 4. The muriatic, and the sulphureous acid gases, expand a little when mingled with nitrous oxide; but they are readily sepa.. rated from it by water. No other aëriform fluids appear to be possessed of the least power of action upon this gas at common temperatures.

Sect. 5. None of the alkaline bodies, except potash and soda, have as yet been combined with nitrous oxide; and even these substances are capable of uniting with it, only when it is in the nascent state.

a. When nitrous oxide in a free state is exposed to the dry alkalies, or alkaline earths, at common temperatures, it is neither absorbed nor acted upon. When it is placed in contact with solutions of them in water, a small quantity of it is dissolved: this phenomenon, however, appears to depend, in a great measure, on the water of the solution; for the gas may be expelled from it unaltered at the temperature of its ebullition.

b. To form the combination of potash, or soda, and nitrous oxide, the alkalies, after being mingled in the dry state with alkaline sulphites, must be exposed, together with them, to nitrous gas.

Dr. Priestley's Experiments and Observations.