adopter tube. Should the retort, indeed, be exposed to a great intensity of flame, the vapour will no doubt be generated with incoercible rapidity, and break the apparatus. But this accident can proceed only from gross imprudence. It resembles, in suddenness, the explosion of gunpowder, and illustrates admirably Dr. Black's observation, that, but for the great latent heat of steam, a mass of water, powerfully heated, would explode on reaching the boiling temperature. I have ascertained that the specific caloric of the vapour of sulphuric acid is very small, and hence the danger to which rash operators may be exposed during its distillation. Hence, also, it is unnecessary to surround the receiver with cold water, as when alcohol and most other liquids are distilled. Indeed the application of cold to the bottom of the receiver generally causes it, in the present operation to crack. By the above method, I have made the concentrated oil of vitriol flow over in a continuous slender stream, without the globe becoming sensibly hot.

I have frequently boiled the distilled acid till only one-half remained in the retort; yet at the temperature of 60° Fahrenheit, I have never found the specific gravity of acid so concentrated, to exceed 1.8455. It is, I believe, more exactly 1.8452. The number 1.850, which it has been the fashion to assign for the density of pure oil of vitriol, is undoubtedly very erroneous, and ought to be corrected. Genuine commercial acid should never surpass 1.8485; when it is denser, we may infer sophistication, or negligence, in the manufacture.

The progressive increase of its density, with saline contamination, will be shown by the following experiments. To 4100 grains of genuine commercial acid (but concentrated to only 1.8350) 40 grains of dry sulphate of potash were added. When the solution was completed, the specific gravity at 60o had become 1.8417. We see that at these densities the addition of 0.01 of salt increases the specific gravity by about 0.0067. To the above 4140 grains other 80 grains of sulphate were added, and the specific gravity, after solution, was found to be 1.8526. We perceive that somewhat more salt is now required to produce a proportional increase of density; 0.01 of the former changing the latter by only 0.0055. Five hundred grains of this acid being evaporated in a platinum capsule left 161⁄2 grains, whence the composition was

Sulphate of potash, with a little sulphate
of lead,

Water of dilution,
Oil of vitriol of 1.8485,

3.30 5.3 91.4

Thus, acid of 1.8526, which in commerce would have been accounted very strong, contained little more than 91 per cent of genuine acid.

Into the last acid more sulphate of potash was introduced, and solution being favoured by digestion in a moderate heat, the specific gravity became, at 60°, 1.9120. of this compound, 300 grains, evaporated in the platinum capsule, left 41 grains of gently ignited saline matter. We have, therefore, nearly 14 per cent. On the specific gravity in this interval, an increase of 0.0054 was effected by 0.01 of sulphate. This liquid was composed of

Saline matter, Water of dilution,

Oil of vitriol of 1.8485,

14.

4.7

81.3

100.0

The general proportion between the density and impurity may be stated at 0.0055 of the former, to 0.01 of the latter.

If from genuine oil of vitriol, containing of a per cent of saline matter, a considerable quantity of acid be distilled off, what remains in the retort will be found very dense. At the specific gravity 1.865, such acid contains 3f of solid salt in the 100 parts. The rest is pure concentrated acid. From such heavy acid, at the end of a few days, some minute crystals will be deposited, after which its specific gravity becomes 1.860, and its transparency is perfect. It contains about 24 per cent of saline matter. Hence if the chemist employ for his researches an acid, which, though originally pretty genuine, has been exposed to long ebullition, he will fall into great errors. From the last experiments it appears, that concentrated oil of vitriol can take up only a little saline matter in comparison with that which is somewhat dilute. It is also evident, that those who trust to specific gravity alone, for ascer taining the value of oil of vitriol, are liable to great impositions.

The saline impregnation exercises an important influence, on all the densities at subsequent degrees of dilution. Thus, the heavy impure concentrated acid, specific gravity 1.8650, being added to water in the proportion of one part to ten, by weight, gave, after twenty-four hours, a compound whose specific gravity was 1.064. But the most concentrated genuine acid, as well as distilled acid, by the same degree of dilution, namely 1+10, acquires the specific gravity of only 1.0602, while that of 1.852, containing, as stated above, 35 per cent of sulphate of potash combined with acid of 1.835, gives, on a similar dilution, 1.058. This difference, though very obvious to good instruments, is inappreciable by ordinary commercial apparatus. Hence this mode of ascertaining the value of an acid, recommended by Mr. Dalton, is inadequate to detect a deterioration of even 8 or 9 per cent. Had a little more salt been present in the acid, the specific gravity of the dilute, in this case, would have equalled that of the genuine. On my acidimeter one per cent of deterioration could not fail to be detected, even by those ignorant of science.

The quantity of oxide, or rather sulphate of lead, which sulphuric acid can take up, is much more limited than is commonly imagined. To the concentrated oil of vitriol I added much carbonate of lead, and after digestion by a gentle heat, in a close vessel, for twenty-four hours, with occasional agitation, its specific gravity, when taken at 60o, was scarcely greater than before the experiment. It contained about 0.005 of sulphate of sulphate lead.

The quantity of water present in 100 parts of concentrated and pure oil of vitriol, seems to be pretty exactly 18 46.

In the experiments executed, to determine the relation between the density of diluted oil of vitriol, and its acid strength, I employed a series of phials, numbered with a diamond. Into each phial, recently boiled acid, and pure water, were mixed in the successive proportions of 99 + 1; 98+2; 97+3; &c. through the whole range of digits down to 1 acid + 99 water. The phials were occasionally agitated during 24 hours, after which the specific gravity was taken. The acid was genuine and well concentrated. Its specific gravity was 1.8485, Some of the phials were kept with their acid contents for a week or two, but no further change in the density took place. The strongest possible distilled acid was employed for a few points, and gave the same results as the other.

Of the three well known modes of as certaining the specific gravity of a liquid, namely, that, by Fahrenheit's hydrometer; by weighing a vessel of known capacity filled with it; and by poising a glass ball, suspended by a fine platina wire from the

arm of a delicate balance; I decidedly prefer the last. The corrosiveness, viscidity, and weight of oil of vitriol, render the first two methods ineligible; whereas, by a ball floating in a liquid, of which the specific gravity does not differ much from its own, the balance, little loaded, retains its whole sensibility, and will give the most accurate consistency of results.

hough the

In taking the specific gravity of concentrated or slightly diluted acid, the temperature must be minutely regulated, because, from the small specific heat of the acid, it is easily affected, and because it greatly influences the density. On removing the thermometer, it will speedily rise in the air to 75° or 80°, though temperature of the apartment be only 60°. Afterwards it will slowly fall to perhaps 60° or 62°. If this thermometer, having its bulb covered with a film of dilute acid (from absorption of atmospheric moisture), be plunged into a strong acid, it will instantly rise 10o, or more, above the real temperature of the liquid. This source of embarrassment and occasional error is obviated by wiping the bulb after every immersion. An elevation of temperature, equal to 10o Fahr. diminishes the density of oil of vitriol by 0.005; 1000 parts being heated from 60° to 212o, become 1.043 in volume, as I ascertained by very careful experiments. The specific gravity, which was 1.848 becomes only 1.772, being the number corresponding to a dilution of 14 per cent of water. The viscidity of oil of vitriol, which below 50o is such as to render it difficult to determine the specific gravity by a floating ball, diminishes very rapidly as the temperature rises, evincing that it is a modification of cohesive attraction.

The following table of densities, corresponding to degrees of dilution, was the result, in each point, of a particular experiment, and was, moreover, verified in a number of its terms, by the further dilution of an acid, having previously combined with it a known proportion of water. The balance was accurate and sensible.

Liq. Sp. Gr. Dry. || Liq. Sp. Gr.

100 1.8485 81.54 99 1.8475 80.72 98 1.8460 79.90 97 1.8439 79.09 96 1.8410 78.28 95 1.8376 77.46 94 1.83.36 76.65 93 1.8290 75.83

75 1.6520 61.15 74 1.6415 60.34 73 1.6321 59.52 72 1.6204 58.71 71 1.6090 57.89 70 1.5975 57.08 69 1.5868 56.26

90 1.8115 73.39

65 1.5390

53.00

40 1.2999 32.61

15 1.1019 12.23

In order to compare the densities of the preceding dilute acid, with those of distilled and again concentrated acid, I mixed one part of the latter with nine of pure water, and after agitation, and a proper interval, to ensure thorough combination, I found its specific gravity as above 1.0682; greater density indicates saline contamination.

Dilute acid having a specific gravity = 1.6321, has suffered the greatest condensation; 100 parts in bulk have become 92.14. If either more or less acid exist in the compound, the volume will be increased. What reason can be assigned for the maximum condensation occuring at this particular term of dilution? The above dilute acid consists of 73 per cent of oil of vitriol, and 27 of water. But 73 of the former contains, by this Table, 59.52 of dry acid, and 13.48 of water. Hence 100 of the dilute acid consist of 59.52 of dry acid, + 13.48 × 3 = 40.44 of water = 99.96; or it is a compound of one atom of dry acid, with three atoms of water. Dry sulphuric acid consists of three atoms of oxygen, united to one of sulphur. Here each atom of oxygen is associated with one of water, forming a symmetrical arrangement. We may therefore infer, that the least deviation from the above definite proportions, must impair the balance of the attractive forces, whence

they will act less efficaciously, and therefore produce less condensation.

The very minute and patient examination which I was induced to bestow on the table of specific gravities, disclosed to me the general law pervading the whole, and consequently the means of inferring at once the density from the degree of dilution, as also of solving the inverse proposition.

If we take the specific gravity, corresponding to ten per cent of oil of vitriol, or 1.0682 as the root; then the specific gravities at the successive terms of 20, 30, 40, &c. will be the successive powers of that root. The terms of dilution are like logarithms, a series of numbers in in arithmetical progression, corresponding to another series, namely, the specific gravities in geometrical progression.

The simplest logarithmic formula which I have been able to contrive is the following.

the specific gravity by 350, the product is directly the per centage of acid.

If the dry acid be sought, we must multiply the logarithm of the specific gravity by 285, and the product will be the an

swer.

Problem 2d, To find the specific gravity corresponding to a given proportion of acid. Multiply the quantity of acid by 2, and divide by 700; the quotient is the logarithm of the specific gravity.

When transmitted through an ignited porcelain tube of one-fith of an inch diameter, it is resolved into two parts of sulphurous acid gas, and one of oxygen gas, with water. Voltaic electricity causes an evolution of sulphur at the negative pole; whilst a sulphate of the metallic wire is formed at the positive. Sulphuric acid has no action on oxygen gas or air. It merely abstracts their aqueous vapour.

Table of distilled sulphuric acid, for the higher points, below which it agrees with the former table.

100

1.846

81.63

If the oxygenized muriatic acid of M. Thenard be put in contact with the sulphate of silver, there is immediately formed insoluble chloride of silver, and oxygenized sulphuric acid. To obtain sul

genation, it is merely necessary to pour barytes-water into the above oxygenized acid, so as to precipitate only a part of it, leaving the rest in union with the whole of the oxygen. Oxygenized sulphuric acid partially reduces the oxide of silver,

occasioning a strong effervescence.

The sulphuric acid strongly attracts water, which it takes from the atmosphere very rapidly, and in larger quantities, if suffered to remain in an open vessel, imbibing one-third of its weight in twentyfour hours, and more than six times its weight in a twelvemonth. If four parts by weight be mixed with one of water at 50°, they produce an instantaneous heat of 300° F.; and four parts raise one of ice to 212°; on the contrary, four parts of ice, mixed with one of acid, sink the thermometer to 4o below 0. When pure it is colourless, and emits no fumes. It requires a great degree of cold to freeze it; and if diluted with half a part or more of water, unless the dilution be carried very far, it becomes more and more difficult to congeal; yet at the specific gravity of 1.78, or a few hundredths above or below this, it may be frozen by surrounding it with melting snow. Its congelation forms regular prismatic crystals with six sides. Its boiling point, point, according to Bergmann, is 540°; according to Dalton, 590°.

* Sulphuric acid consists of three prime equivalents of oxygen, one of sulphur, and one of water; and by weight, therefore, of 3.0 oxygen + 2.0 sulphur + 1.125 water = 6.125, which represents the prime equivalent of the concentrated liquid acid; while 3+2 5, will be that of

the dry acid.

Pure sulphuric acid is without smell and colour, and of an oily consistence. Its action on litmus is so strong, that a single drop of acid will redden an immense quantity. It is a most violent caustic; and has sometimes been administered with the most criminal purposes. The person who unfortunately swallows it, speedily dies in dreadful agonies and convulsions. Chalk, or common carbonate of magnesia, is the best antidote for this, as well as for the strong nitric and muriatic acids.

All the simple combustibles decompose sulphuric acid, with the assistance of heat. About 400o Fahr. sulphur, converts sulphuric into sulphurous acid. Several metals at an elevated temperature decompose this acid, with evolution of sulphurous acid gas, oxidizement of the metal, and combination of the oxide, with the undecomposed portion of the acid.*

The sulphuric acid is of very extensive use in the art of chemistry, as well as in metallurgy, bleaching, and some of the processes for dyeing; in medicine it is given as a tonic, stimulant, and lithontriptic, and sometimes used externally as a caustic.

The combinations of this acid with the various bases are called sulphates, and most of them have long been known by various names. With barytes it is found native and nearly pure in various forms, in coarse powder, rounded masses, stalactites, and regular crystallizations, which are in some lamellar, in others needly, in others prismatic or pyramidal. The cawks of our country and the Bolognian stone are merely native sulphates of barytes. Their colour varies considerably as well as their figure, but their specific gravity is great, that of a very impure kind being 3.89, and the pure sorts varying from 4 to 4.865; hence it has been distinguished by the names of marmor metallicum and ponderous spar.

* It consists, according to Dr. Wollaston, of 5 parts of dry acid, and 9.75 of barytes; and by Professor Berzelius's last estimate, of 5 of acid and 9.573 barytes.*

This salt, though deleterious, is less so than the carbonate of barytes, and is more economical for preparing the muriate for medicinal purposes. It requires 43.000 parts of water to dissolve it at 60°.

Sulphate of strontian has a considerable resemblance to that of barytes in its properties. It is found native in considerable quantities at Aust Passage and other places in the neighbourhood of Bristol. It requires 3840 parts of boiling water to dissolve it.

* Its composition is 5 acid + 6.5 base.* The sulphate of potash, vitriolated kali of the London college, formerly vitriolated tartar, sal de duobus, and arcanum duplicatum, crystallizes in hexaëdral prisms, terminated by hexagonal pyramids, but susceptible of variations. Its crystallization by quick cooling is confused. Its taste is bitter, acrid, and a little saline. It is soluble in 5 parts of boiling water, and 16 parts at 60o. In the fire it decrepitates, and is fusible by a strong heat. It is decomposable by charcoal at a high temperature. It may be prepared by direct mixture of its component parts; but the usual and cheapest mode is to neutralize the acidulous sulphate left after distilling nitric acid, the sal enixum of the old chemists, by the addition of carbonate of potash. The sal polychrest of old dispensatories, made by deflagrating sulphur and nitre in a crucible, was a compound of the sulphate and sulphite of potash. The acidulous sulphate is sometimes employed as a flux, and likewise in the manufacture of alum. In medicine the neutral salt is sometimes used as a deobstruent, and in large doses as a mild cathartic; dissolves in a considerable portion of water, and taken daily in such quantity as to be gently aperient, it has been found serviceable in cutaneous affections, and is sold in London for this purpose as a nostrum; and certainly it de serves to be distinguished from the generality of quack medicines, very few indeed of which can be taken without imminent hazard.

* It consists of 5 acid + 5.95 base; but there is a compound of the same constituents, in the proportion of 10 acid + 5.95 potash, called the bisulphate.*

The sulphate of soda is the vitriolated natron of the college, the well known Glauber's salt, or sal mirabile. It is commonly prepared from the residuum left after distilling muriatic acid, the superfluous acid of which may be saturated by the addition of soda, or precipitated by lime; and is likewise obtained in the manufacture of the muriate of ammonia. (See AMMONIA). Scherer mentions another mode by Mr. Funcke, which is, making 8 parts of calcined sulphate of lime, 5 of clay, and 5 of common salt, into a paste with water; burning this in a kiln; and then powdering, lixiviating, and crystallizing. It exists in large quantities under the surface of the earth in some countries, as Persia, Bohemia, and Switzerland; is found mixed with other substances in mineral springs

and sea water; and sometimes effloresces on walls. Sulphate of soda is bitter and saline to the taste. It is soluble in 2.85 parts of cold water, and 0.8 at a boiling heat; it crystallizes in hexagonal prisms bevelled at the extremities, sometimes grooved longitudinally, and of very large size, when the quantity is great: these effloresce completely into a white powder if exposed to a dry air, or even if kept wrapped up in paper in a dry place; yet they retain sufficient water of crystallization to undergo the aqueous fusion on exposure to heat, but by urging the fire, melt. Barytes and strontian take its acid from it entirely, and potash partially; the nitric and muriatic acids, though they have a weaker affinity for its base, combine with a part of it when digested on it. Heated with charcoal its acid is decomposed. As a purgative its use is very general; and it has been employed to furnish soda. Pajot des Charmes has made some experiments on it in fabricating glass: with sand alone it would not succeed, but equal parts of carbonate of lime, sand, and dried sulphate of soda, produced a clear, solid, pale, yellow glass.

* It is tis composed of 5 acid + 3.95 base + 11.25 water in crystals; when dry, the former two primes are its constituents.* Sulphate of soda and sulphate of ammonia form together a triple salt.

Sulphate of lime, selenite, gypsum, plaster of Paris, or sometimes alabaster, forms extensive strata in various mountains. The specular gypsum, or glacies Mariæ, is a species of this salt, and affirmed by some French travellers to be employed in Russia, where it abounds, as a substitute for glass in windows. Its specific gravity is from 1.872 to 2.311. It requires 500 parts of cold water, and 450 of hot, to dissolve it. When calcined it decrepitates, becomes very friable and white, and heats a little with water, with which it forms a solid mass. In this process it loses its water of crystallization. In this state it is found native in Tyrol, crystallized in rectangular parallelopipeds, or octaëdral or hexaedral prisms, and is called anhydrous sulphate of lime. Both the natural and artificial anhydrous sulphate consists of 56.3 lime and 43.6 acid, according to Mr. Chenevix. The calcined sulphate is much employed for making casts of anatomical and ornamental figures; as one of the bases of stucco; as a fine cement for making close and strong joints between stone, and joining rims or tops of metal to glass; for making moulds for the Staffordshire potteries; for cornices, mouldings, and other ornaments in building. For these purposes, and for being wrought into columns, chimney-pieces, and various ornaments, about eight hundred tons are raised annu