Obrazy na stronie
PDF
ePub
[ocr errors]

iron, it forms sulphate of iron or copperas, which constitutes a metallic salt. In order to show the differ. ence between alkaline, earthy, and metallic salts, the following experiments may be useful:

Experiment 1. If into a fluid, prussiate of potash, tincture of galls, or a solution of potash be dropped, which is followed by a dark coloured precipitate, the presence of metallic matter may be inferred, indicating a metallic salt.

Rationale. If metal be present, prussiate of potash will cause a peculiar coloured precipitate, as blue with

iron, forming a metallic prussiate; tincture of galls Es will also strike a particular colour; and potash pre

cipitates the metal in the form of oxyd.

Experiment 2. If a solution of salt in which prussiate of potash occasions no precipitate, affords a

copious white precipitate by the addition of carbonate E of potash, the salt has an earth for its base, and therefore belongs to the class of earthy salts.

Rationale. The acid which holds the earth in solution, unites with the alkali of the carbonate, and the $ carbonic acid passes to the earth, forming a carbonated earth.

Experiment 3. If carbonate of potash be added to a fluid known to contain a salt in solution, and no precipitation takes place, the presence of an alkaline salt is inferred.

Rationale. As the acid is already combined with an alkali, it is obvious, that as no decomposition can take place by the addition of potash, and that the alkali itself is not precipitated, no effect will ensue.

Mr. Parke has given the following beautiful experiments in illustration of the nature of saline bodies :

Experiment 4. Pour a little sulphuric acid into a solution of soda in water, evaporate the superfluous water, and then notice the crystallization of the newformed salt. If the liquor be allowed to stand quietly for a few hours in a cool place, the salt will be seen to shoot into beautiful crystals of sulphate of soda.

Experiment 5. Dissolve some magnesia in diluted sulphuric acid, so as to saturate the acid. Pour off the

T

[ocr errors]

clear liquid, and evaporate a portion of the superfluous water. If the remainder be suffered to cool, a crystallized salt will be formed, similar in every respect to Epsom salt.

Experiment 6. Put about half an ounce of quicksilver into an oil flask, and pour about an ounce of diluted nitrous acid upon it. The nitrous acid will be decomposed by the metal with astonishing rapidity ; the bulk of the acid will be quickly changed to a beautiful green, while its surface exhibits a dark crimson ; and an effervescence indescribably vivid and pleasing will go on during the whole time the acid operates upon the quicksilver. When a part only of the metal is dissolved, a change of colour will again take place, and the acid by degrees will become paler, till it is as pellucid as pure water. This is one instance of a metallic solution by means of an acid ; in which the opacity of a metallic body is completely overcome, and the whole rendered perfectly transparent.

Experiment 7. Take the metallic solution formed in the last experiment, add a little more quicksilver to saturate the acid ; then place it at some distance, over the flame of a lamp, so as gently to evaporate a part of the water. The new formed salt will soon be seen to begin to shoot into needle-like prismatic crystals, crossing each other in every possible direction; affording an instance of the formation of a metallic salt.

We shall first notice the alkaline salts, then the earthy salts, and lastly the metallic salts. With respect to the number of these saline combinations, it would appear, that having 32 acids and 57 bases, there must be 1824 salts : but there are several of the me. tallic oxyds which cannot conibine with many of the acids; which is also the case with silica, one of the earths. However, to compensate for this deficiency, there are several acids capable of combining with two bases at once. These, we have said, are called triplesalts. Besides these there are also super-salts and subsalts.

DIVISON I.

ALKALINE SALTS.

SECTION I.

SALTS OF POTASH.

MURIATE OF POTASH.

Experiment l. If muriatic acid be saturated with · potash, and the fluid evaporated, muriate of potash will form and crystallize in irregular cubes.

Remark. This salt is soluble in three times its weight of cold water. It melts in a red heat, and loses about three per cent. of its weight. It is the same as the febrifuge salt of sylvius. It contains near 30 per cent. of acid. It is found in sea water, in old plasa ter, and in vegetable and animal fluids. It constitutes the greater part of the soap-boilers liquor, after the formation of hard soap. See Soap.

Experiment 2. If sulphuric acid be added to muri. ate of potash, white acrid fumes, or muriatic acid gas, will be disengaged.

Rationale. The sulphuric acid unites with the potash, forming sulphate of potash, and the muriatic acid is evolved.

FLUATE OF POTASH.

Experiment 1. If fuoric acid be saturated with potash fluate of potash will result.

Remark. This salt is hardly known. It is a gelatinous substance, which is deliquescent, and readily soluple in water. It combines with silica, into a white powder.

Experiment 2. If lime water be added to fluate of potash, a precipitate will be formed analogous in composition to the native fluor spar.

Rationale. The fluoric acid in part quits the pot. ash, and unites with the lime, forming fluate of lime.

Experiment 3. If sulphuric acid be poured on fluate of potash, fluoric acid gas will be disengaged.

Rationale. The sulphuric acid unites with the potash into a sulphate of potash, and the fluoric acid is separated.

BORATE OF POTASH.

Experiment 1. If boracic acid be saturated with potash, a compound will be formed called borate of potash, a salt not much known.

Experiment 2. If this salt, dissolved in water to saturation, be mingled with a small quantity of sulphuric acid, boracic acid will separate as the liquor cools.

Rationale. The sulphuric acid unites with the potash, and the boracic acid is disengaged.

PHOSPHATE OF POTASH.

Experiment 1. If-carbonate of potash be added to phosphoric acid till all the effervescence cease, and the solution then evaporated, crystals of superphosphate of potash will form in striated prisms; and,

Experiment 2. If the superphosphate be saturated with potash, and the mixture exposed to heat in a platinum crucible, the phosphate of potash will be prepared.

Experiment 3. If the sale thus formed, be dissolved in nitric acid, and the solution decomposed by lime

water or ainmonia, the phosphate will be precipitated.

Rationale. The lime or alkali added, unites with the nitric acid, by which the phosphate is disengaged. The solution, in order to decompose it, must some. times be heated. The phosphate contains 100 acid, and 164 base.

PHOSPHITE OF POTASH.

Experiment 1. If phosphorous acid be combined with potash, a phosphite of potash will result.

Remark. This salt crystallizes in four sided prisms, and possesses a sharp, saline taste.

CARBONATE OF POTASH.

Experiment 1. If carbonic acid gas be passed through a solution of potash, till the salt crystallizes, carbonate of potash, or the super carbonate of some, will be formed.

Remark. The union of potash with carbonic acid to a maximum forms, therefore, a salt, which crystallizes in rhomboidal prisms, with dihedral summits, having an alkaline taste, and still gives a green colour to vegetable blues. This preparation is known also by the name of æraled potash, or ærated vegetable alkali. It contains 100 acid, 95 base, and 37 water.

Experiment 2. If 120 grains of potash be dissolved in 20 ounces of water, and combined with carbonic acid to the quantity of 6 times the volume of the water, the arated putash water of the French will be formed.

Experiment. 3. If one ounce of pearl-ash be dissolved in ten pounds of water, and the solution saturated with carbonic acid, either in a Nooth's or Woulf's apparatus, or more conveniently in the apparatus lately invented by Mr. Hembel of this city, the solution of super carbonate of potash of the Edinburgh college will be formed.

« PoprzedniaDalej »