Liq. Dry

Liq. Dry

Liq. Dry

in 100 in 100.

1.5000 100 79.700 1.4189

1.4980 99 78.903 1.4147 1.4960 98 78.106 1.4107

1.4940 97 77.309 1.4065

1.4910 96 76.512 1.4023

1.4880 95 75.715 1.3978

1.4850 94 74.918 1.3945

1.4820 93 74.121 1.3882

1.4790 92 73.324 1.3833

1.4760 91 72.527 1.3783

1.4730 90 71.730 1.3732

1.4700 89 70.933 1.3681

in 100 in 100.

in 100 in 100.

70 55.790 69 54.993

1.2644

1.2583

45 35.865 1.1109 20 15.940 44 35.068 1.1051 19 15.143

43 34.271 1.0993 18 14.346

42 33.474 1.0935 17 13.549

41 32.677 1.0878 16 12.752

40 31.880 1.0821 15 11.955

39 31.083 1.0764 14 11.158

1.4640 87 69.339 1.3579

1.4600 86 68.542 1.3529

61 48.617

1.2084

36 28.692

1.0595

11

8.767

1.4500 83 66.155 1.3376

The column of dry acid shows the weight which any salifiable base would gain, by uniting with 100 parts of the liquid acid of the corresponding specific gravity. But it may be proper here to observe, that Sir H. Davy, in extending his views rela tive to the constitution of the dry muriates, to the nitrates, has suggested, that the latter when dry may be considered as consisting, not of a dry nitric acid combined with the salifiable oxide, but of the oxygen and nitrogen of the nitric acid with the metal itself in triple union. A view of his reasoning will be found under the article SALT. He regards liquid nitric acid at its utmost density as a compound of 1 prime of hydrogen, 1 of nitrogen, and 6 of oxygen.*

The strongest acid that Mr. Kirwan could procure at 60° was 1.5543; but Rouelle professes to have obtained it of 1.583.

Nitric acid should be of the specific gravity of 1.5, or a little more, and colourless.

* That of Mr. Kirwan seems to have consisted of one prime of real acid and one of water, when the suitable corrections are made; but no common chemical use requires it of such a strength. The following table of boiling points has been given by Mr. Dalton.

At 1.42 specific gravity it distils unaltered. Stronger acid than that becomes weaker, and weaker acid stronger, by boiling. When the strong acid is cooled down to-60°, it concretes, by slight agitation, into a mass of the consistence of butter.

This acid is eminently corrosive, and hence its old name of aquafortis. Its taste is sour and acrid It is a deadly poison when introduced into the stomach in a concentrated state; but when greatly diluted, it may be swallowed without inconvenience. It is often contaminated, through negligence or fraud in the manufacturer, with sulphuric and muriatic acids. Nitrate of lead detects both, or nitrate of barytes may be employed to determine the quantity of sulphuric acid, and nitrate of silver that of the muriatic. The latter proceeds from the crude nitre usually containing a quantity of common salt.*

When it is passed through a red hot porcelain tube, it is resolved into oxygen

26 20.722 1.0053

1

0.797

and nitrogen, in the proportion above stated. It retains its oxygen with little force, so that it is decomposed by all combustible bodies. Brought into contact with hydrogen gas at a high temperature, a violent detonation ensues, so that this must not be done without great caution. It inflames essential oils, as those of tur

pentine and cloves, when suddenly poured

on them; but, to perform this experiment with safety, the acid must be poured out of a bottle tied to the end of a long stick, otherwise the operator's face and eyes will be greatly endangered. If it be poured on perfectly dry charcoal powder, it excites combustion, with the emission of copious fumes. By boiling it with sulphur it is decomposed, and its oxygen,

uniting with the sulphur, forms sulphuric

acid. Chemists in general agree, that it

acts very powerfully on almost all the metals; but Baumé has asserted, that

it

will not dissolve tin, and Dr. Woodhouse

of Pennsylvania affirms, that in a highly concentrated and pure state it acts not at all on silver, copper, or tin. though, with the addition of a little water, its action on them is very powerful.

* Proust has ascertained, that acid having the specific gravity 1.48, has no more action on tin than on sand, while acid somewhat stronger or weaker acts furiously on the metal. Now, acid of 1.485, by Dr. Ure's table, consists of one prime of real acid united with two of water, constituting,

at-40°.3. The first has of 1.330 nearly, and con

specific gravity

sists of 1 prime of dry acid + 7 of water; the second has a specific gravity of 1.420, and contains exactly one prime of dry

acid + four of water; while the third has a specific gravity of 1.215, consisting of one prime of acid + 14 of water. We perceive, that the liquid acid of 1.420, composed of 4 primes of water + one of

dry acid, possesses the greatest power of

resisting the influence of temperature to change its state. It requires the maximum heat to boil it, when it distils unchanged; and the maximum cold to effect its con

gelation.*

It has already been observed, that the nitric acid, when first distilled over, holds in solution a portion of nitric oxide, which is greater in proportion as the heat has been urged toward the end, and much increased by even a small portion of inflammable matter, should any have been present. The colour of the acid, too, is affected by the quantity of nitric oxide it holds, and Sir H. Davy has given us the following table of proportions answering

to its different hues.

Blue green

84.6

But these colours are not exact indications of the state of the acid, for an addition of water will change the colour into one lower in the scale, so that a considerable portion of water will change the dark orange to a blue green.

The nitric acid is of considerable use in the arts. It is employed for etching on copper; as a solvent of tin to form with that metal a mordant for some of the finest dyes; in metallurgy and assaying; in various chemical processes, on account of the facility with which it parts with oxygen and dissolves metals; in medicine as a tonic, and as a substitute for mercurial preparations in syphilis and affections of the liver; as also in form of vapour to destroy contagion. For the purposes of the arts it is commonly used in a diluted state, and contaminated with the sulphuric and muriatic acids, by the name of aquafortis. This is generally prepared by mixing [10]

VOL. I.

7.76

8.

8.10

7.6

7.55

7.5

7.44

7.4

common nitre with an equal weight of sulphate of iron, and half its weight of the same sulphate calcined, and distilling the mixture; or by mixing nitre with twice its weight of dry powdered clay, and distilling in a reverberatory furnace. Two kinds are found in the shops, one called double aquafortis, which is about half the strength of nitric acid; the other simply aquafortis, which is half the strength of the double.

A compound made by mixing two parts of the nitric acid with one of muriatic, known formerly by the name of aqua regia, and now by that of nitro-muriatic acid, has the property of dissolving gold and platina. On mixing the two acids, heat is given out, an effervescence takes place, and the mixture acquires an orange colour. This is likewise made by adding gradually to an ounce of powdered muriate of ammonia, four ounces of double aquafortis, and keeping the mixture in a sandheat till the salt is dissolved; taking care to avoid the fumes as the vessel must be left open; or by distilling nitric acid with an equal weight, or rather more, of common salt.

* On this subject we are indebted to Sir. H. Davy for some excellent observations, published by him in the first volume of the Journal of Science. If strong nitrous acid, saturated with nitrous gas, be mixed with a saturated solution of muriatic acid gas, no other effect is produced than might be expected from the action of nitrous acid of the same strength on an equal quantity of water; and the mixed acid so formed has no power of action on gold or platina. Again, if muriatic acid gas, and nitrous gas in equal volumes, be mixed together over mercury, and half a volume of oxygen be added, the immediate condensation will be more than might be expected from the formation of nitrous acid gas. And when this is decomposed, or absorbed by the mercury, the muriatic acid gas is found unaltered, mixed with a certain portion of nitrous gas.

It appears then that nitrous acid, and muriatic acid gas, have no chemical action on each other. If colourless nitric acid, and muriatic acid of commerce, be mixed together, the mixture immediately becomes yellow, and gains the power of dissolving gold and platinum. If it be gently heated, pure chlorine arises from it, and the coIour becomes deeper. If the heat be longer continued, chlorine still rises, but mixed with nitrous acid gas. When the process has been very long g continued till the colour becomes very deep, no more chlorine can be procured, and it loses its power of acting upon platinum and gold. It is now nitrous and muriatic acid. It appears then from these observations, which have been very often repeated, that nitro-muriatic acid owes its peculiar properties to a mutual decomposition of the nitric and muriatic acids; and that water, chlorine, and nitrous acid gas, are the results. Though nitrous gas and chlorine have no action on each other when perfectly dry, yet if water be present there is an immediate decomposition, and nitrous acid and muriatic acid are formed. 118 parts of strong liquid nitric acid being decomposed in this case, yield 67 of chlorine. Aqua regia does not oxidize gold and platina. It merely causes their combination with chlorine.

A bath made of nitro-muriatic acid, diluted so much as to taste no sourer than vinegar, or of such a strength as to prick the skin a little, after being exposed to it for twenty minutes or half an hour, has been introduced by Dr. Scott of Bombay as a remedy in chronic syphilis, a variety

of ulcers, and diseases of the skin, chronic hepatitis, bilious dispositions, general debility, and languor. He considers every trial as quite inconclusive, where a ptyalism, some affection of the gums, or some very evident constitutional effect, has not arisen from it. The internal use of the same acid has been recommended to be conjoined with that of the partial or general bath.*

With the different bases the nitric acid forms nitrates.

The nitrate of barytes, when perfectly pure, is in regular octaëdral crystals, though it is sometimes obtained in small shining scales. It may be prepared by uniting barytes directly with nitric acid, or by decomposing the carbonate or sulphuret of barytes with this acid. Exposed to heat it decrepitates, and at length gives out its acid, which is decomposed; but if the heat be urged too far, the barytes is apt to vitrify with the earth of the crucible. It is soluble in 12 parts of cold, and 3 or 4 of boiling water. It is said to exist in some mineral waters. * It consists of 6.75 acid + 9.75, or 9.7 base.*

The nitrate of potash is the salt well known by the name of nitre or saltpetre. It is found ready formed in the East Indies, in Spain, in the kingdom of Naples, and elsewhere, in considerable quantities; but nitrate of lime is still more abundant. Far the greater part of the nitrate made use of is produced by a combination of circumstances which tend to compose and condense nitric acid. This acid appears to be produced in all situations, where animal matters are completely decomposed, with access of air and of proper substances with which it can readily combine. Grounds frequently trodden by cattle and impregnated with their excrements, or the walls of inhabited places where putrid animal vapours abound, such as slaughterhouses, drains, or the like, afford nitre by long exposure to the air. Artificial nitre beds are made by an attention to the circumstances in which this salt is produced by nature. Dry ditches are dug, and covered with sheds, open at the sides, to keep off the rain: these are filled with animal substances such as dung, or other excrements, with the remains of vegetables, and old mortar, or other loose calcareous earth; this substance being found to be the best and most convenient receptacle for the acid to combine with. Occasional watering, and turning up from time to time, are necessary, to accelerate the process, and increase the surfaces to which the air may apply; but too much moisture is hurtful. When a certain portion of nitrate is formed, the process appears to go on more quickly; but a certain quantity stops it altogether, and after this cessation the materials will go on to furnish more,

if what is formed be extracted by lixiviation. After a succession of many months, more or less, according to the management of the operation, in which the action of a regular current of fresh air is of the greatest importance, nitre is found in the mass. If the beds contained much vegetable matter, a considerable portion of the nitrous salt will be common saltpetre, but, if otherwise, the acid will, for the most part, be combined with the calcareous earth. * It consists of 6.75 acid + 5.95 potash.*

To extract the saltpetre from the mass of earthy matter, a number of large casks are prepared, with a cock at the bottom of each, and a quantity of straw within, to prevent its being stopped up. Into these the matter is put, together with woodashes, either strewed at top, or added during the filling. Boiling water is then poured on, and suffered to stand for some time; after which it is drawn off, and other water added in the same manner, as long as any saline matter can be thus extracted. The weak brine is heated, and passed through other tubs, until it becomes of considerable strength. It is then carried to the boiler, and contains nitre and other salts; the chief of which is common culinary salt, and sometimes muriate of magnesia. It is the property of nitre to be much more soluble in hot than cold water; but common salt is very nearly as soluble in cold as in hot water. Whenever, therefore, the evaporation is carried by boiling to a certain point, much of the common salt will fall to the bottom, for want of water to hold it in solution, though the nitre will remain suspended by virtue of the heat. The common salt thus separated is taken out with a perforated ladle, and a small quantity of the fluid is cooled, from time to time, that its concentration may be known by the nitre which crystallizes in it. When the fluid is sufficiently evaporated, it is taken out and cooled, and great part of the nitre separates in crystals; while the remaining common salt continues dissolved, because equally soluble in cold and in hot water. Subsequent evaporation of the residue will separate more nitre in the same manner. * By the suggestion of Lavoisier, a much simpler plan was adopted; reducing the crude nitre to powder, and washing it twice with water.* This nitre, which is called nitre of the first boiling, contains some common salt; from which it may be purified by solution in a small quantity of water, and subsequent evaporation; for the crystals thus obtained are much less contaminated with common salt than before; because the proportion of water is so much larger, with respect to the small quantity contained by the nitre, that very little of it

will crystallize. For nice purposes, the solution and crystallization of nitre are repeated four times. The crystals of nitre are usually of the form of six-sided flattened prisms, with diedral summits. Its taste is penetrating; but the cold produced by placing the salt to dissolve in the mouth is such as to predominate over the real taste at first. Seven parts of water dissolve two of nitre, at the temperature of sixty degrees; but boiling water dissolves its own weight. 100 parts of alcohol, at a heat of 176°, dissolve only 2.9.

On being exposed to a gentle heat, nitre fuses; and in this state being poured into moulds, so as to form little round cakes, for balls, it is called sal prunella, or crystal mineral. This at least is the way in which this salt is now usually prepared, conformably to the directions of Boerhaave; though in most dispensatories a twenty-fourth part of sulphur was directed to be deflagrated on the nitre before it was poured out. This salt should not be left on the fire after it has entered into fusion, otherwise it will be converted into a nitrite of potash. If the heat be increased to redness, the acid itself is decomposed, and a considerable quantity of tolerably pure oxygen gas is evolved, succeeded by nitrogen.

This salt powerfully promotes the combustion of inflammable substances. Two or three parts mixed with one of charcoal, and set on fire, burn rapidly; azote and carbonic acid gas are given out, and a small portion of the latter is retained by the alkaline residuum, which was formerly called clyssus of nitre. Three parts of nitre, two of subcarbonate of potash, and one of sulphur, mixed together in a warm mortar, form the fulminating powder; a small quantity of which, laid on a fire-shovel, and held over the fire till it begins to melt, explodes with a loud sharp noise. Mixed with sulphur and charcoal, it forms gunpowder. See GUNPOWDER.

Three parts of nitre, one of sulphur, and one of fine saw-dust, well mixed, constitute what is called the powder of fusion. If a bit of base copper be folded up and covered with this powder in a walnutshell, and the powder be set on fire with a lighted paper, it will detonate rapidly, and fuse the metal into a globule of sulphuret, without burning the shell.

If nitrate of potash be heated in a retort with half its weight of solid phosphoric or boracic acid, as soon as this acid begins to enter into fusion, it combines with the potash, and the nitric acid is expelled, accompanied with a small portion of oxygen gas and nitric oxide.

Silex, alumina, and barytes, decompose this salt in a high temperature by uniting with its base. The alumina will effect

this even after it has been made into pottery.

The uses of nitre are various. Beside those already indicated, it enters into the composition of fluxes, and is extensively employed in metallurgy; it serves to promote the combustion of sulphur in fabricating its acid; it is used in the art of dyeing; it is added to common salt for preserving meat, to which it gives a red hue; it is an ingredient in some frigorific mixtures; and it is prescribed in medicine, as cooling, febrifuge, and diuretic; and some have recommended it mixed with vinegar as a very powerful remedy for the sea scurvy.

Nitrate of soda, formerly called cubic or quadrangular nitre, approaches in its properties to the nitrate of potash; but differs from it in being somewhat more soluble in cold water, though less in hot, which takes up little more than its own weight; in being inclined to attract moisture from the atmosphere; and in crystallizing in rhombs, or rhomboidal prisms. It may be prepared by saturating soda with the nitric acid; by precipitating nitric solutions of the metals, or of the earths, except barytes, by soda; by lixiviating and crystallizing the residuum of common salt distilled with three-fourths its weight of nitric acid; or by saturating the mother waters of nitre with soda instead of potash. This salt has been considered as useless; but professor Proust says, that five parts of it, with one of charcoal and one of sulphur, will burn three times as long as common powder, so as to form an economical composition for fire-works. *It consists of 6.75 acid + 3.95 soda.*

Nitrate of strontian may be obtained in the same manner as that of barytes, with which it agrees in the shape of its crystals, and most of its properties. It is much more soluble, however, requiring but four or five parts of water according to Vauquelin, and only an equal weight according to Mr. Henry. Boiling water dissolves nearly twice as much as cold. Applied to the wick of a candle, or added to burning alcohol, it gives a deep red colour to the flame. On this account it may be useful, perhaps, in the art of pyrotechny. *It consists of 6.75 acid + 6.5 strontian. *

Nitrate of lime, the calcareous nitre of

older writers, abounds in the mortar of old buildings, particularly those that have been much exposed to animal effluvia, or processes in which azote is set free. Hence it abounds in nitre beds, as was observed when treating of the nitrate of potash. It may also be prepared artificially, by pouring dilute nitric acid on carbonate of lime. If the solution be boiled down to a sirupy consistence, and exposed in a cool place, it crystallizes in long prisms,

resembling bundles of needles diverging from a centre. These are soluble, according to Henry, in an equal weight of boiling water, and twice their weight of cold; soon deliquesce on exposure to the air, and are decomposed to a red heat. Fourcroy says, that cold water dissolves four times its weight, and that its own water of crystallization is sufficient to dissolve it at a boiling heat. It is likewise soluble in less than its weight of alcohol. By evaporating the aqueous solution to dryness, continuing the heat till the nitrate fuses, keeping it in this state five or ten minutes, and then pouring it into an iron pot previously heated, we obtain Baldwin's phosphorus. This, which is perhaps more properly nitrite of lime, being broken to pieces, and kept in a phial closely stopped, will emit a beautiful white light in the dark, after having been exposed some time to the rays of the sun. At present no use is made of this salt, except for drying some of the gases by attracting their moisture; but it might be employed instead of the nitrate of potash for manufacturing aquafortis.

The nitrate of ammonia possesses the property of exploding, and being totally decomposed, at the temperature of 600°; whence it acquired the name of nitrum flammans. The readiest mode of preparing it is by adding carbonate of ammonia to dilutet nitric acid till saturation takes place. If this solution be evaporated in a heat between 70° and 100o, and the evaporation not carried too far, it crystallizes in hexaëdral prisms terminating in very acute pyramids: if the heat rise to 212o, it will afford, on cooling, long fibrous silky crystals: if the evaporation be carried so far as for the salt to concrete immediately on a glass rod by cooling, it will form a compact mass. According to Sir H. Davy, these differ but little from each other, except in the water they contain, their component parts being as follows: