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tions of magnesium salts, which must be here explained, as it is the type of a reaction which will be found to occur frequently between hydrate of ammonium and the salts of other metals. .

This reaction has its foundation in the fact that salts of ammonium containing strong acid-radicals, as Cl and Sox, form double salts with magnesium salts, and that from these double salts the magnesium cannot be precipitated by the addition of hydrate of ammonium in excess. The hydrate of ammonium acts in the first place by ordinary decomposition upon a magnesium salt, producing the hydrate of magnesium ; but in so doing a salt of ammonium must be simultaneously formed, corresponding to the original magnesium salt; thusMgCl+NH HO=NH,Cl+MgHO.

Precipitate. The chloride of ammonium thus produced then unites with another equivalent of chloride of magnesium (supposing more to be present); and upon the double salt so formed (MgCl, NH,Cl) any excess of hydrate of ammonium will exert no decomposing action. Hydrate of ammonium, therefore, when added in excess to a solution of a magnesium salt, can never precipitate more than one-half of the magnesium ; and for every two equivalents present, the following will be the decomposition :2MgCl+2NHHO=MgCl, NH,Cl+MgO+NHHO.

Soluble double Precipitate.

salt. It is obvious from this, that if excess of ammonium salt is subsequently added, even that portion of the hydrate of magnesium formed will be perfectly dissolved, because

MgHO+2NH4Cl=NH HO+MgCl, NH,C. The hydrates of barium, strontium, and calcium being more soluble than the hydrate of magnesium, also produce the hydrate when added to magnesium salts.

The formula of the salt dried at 100° C. is MgHO.

It dissolves readily in salts of ammonium and in 55,368 parts of cold or boiling water; it is easily decomposed and dissolved by almost every acid.

THE SULPHATE is extremely soluble.

The Carbonate is produced by the action of neutral carbonate of potassium (K, CO2) on solutions of magnesium salts. The neutral carbonate of ammonium does not produce an immediate precipitate, but after boiling the solution or allowing it to stand, a portion of the magnesium is precipitated. It is a bulky white precipitate.

The formula of this salt is variable, on account of its not being the neutral carbonate, but a mixed carbonate and hydrate; it is sometimes 2(MgHO), 3(Mg, CO3)+3aq, and sometimes MgHO, 2(Mg, CO3)+2aq. The reaction which results in its formation is not so simple as those previously given ; it is as follows:

8(MgCl)+4(Na, CO2)+4(H,0)=2(MgHO),

3(Mg, C0z), 3aq +8NaCl+CO The precipitate is increased by boiling, because then the carbonic acid escapes which has been keeping a portion of the magnesium in solution as acid carbonate (MgHCO), which, in common with the other acid carbonates of this subdivision, and all salts of similar composition, is perfectly soluble in cold water, but is decomposed directly the temperature is raised, with precipitation of neutral carbonate and evolution of carbonic acid gas.

The formula of the salt produced by very great excess of neutral carbonate of ammonium ([NH,],CO2), is MgNH,CO+2aq; the precipitation of the magnesium is said to be complete. This precipitate is quite soluble in pure water if cold, but from the solution when boiled, neutral carbonate of magnesium is precipitated, the neutral carbonate of ammonium volatilizing at the same time; thus

2(MgNH,CO3)=Mg, CO, +(NH.),CO..

Precipitate. Both the above-described precipitates are instantly dissolved by solutions of ammonium salts. The first of them is somewhat soluble in excess of cold solutions of its precipitants, and in most other sodium and potassium salts, as chloride, sulphate, and nitrate. It requires 2493 parts of cold, and 9000 of boiling

water for its solution. Both salts are readily decomposed and dissolved by almost every acid, but are dissolved with formation of the acid salt by solutions of carbonic acid gas (CO2).

THE OXALATE is soluble, unless the oxalic acid or soluble oxalate employed is added to very concentrated solutions of magnesium salts, or the mixture allowed to stand for some time; the precipitate is easily dissolved by ammonium salts and acids.

THE FERROCYANIDE is produced by the action of ferrocyanide of potassium (K, Cfy) after long standing or by rapidly boiling : its precipitation is also immediately induced by the action of chloride of ammonium (NH, CI).

Its formula is Mg, Cfy + haq; but when an ammonium salt is present, the salt appears to be MgNH, Cfy.

It is insoluble in chloride of ammonium, but is dissolved immediately by hydrochloric acid.

THE PHOSPHATE is produced by the action of phosphate of sodium (Na, HPO) on solutions of magnesium salts, and is slowly precipitated. It is white and crystalline. Its formula is Mg, HPO, +7aq. It is insoluble in ammonium salts : it dissolves in 322 parts of cold water, but is less soluble in boiling water: it is said to decompose on boiling. In acids it is immediately soluble.

If hydrate of ammonium (NH, HO) be present in a solution of magnesium salt when the phosphate of sodium is added, the latter salt becomes one of the most delicate tests for the presence of magnesium, which is then completely precipitated from its solutions in ammonium salts (the double salts before mentioned), from which no other reagent in common use will separate it. · The Phosphate of Magnesium and Ammonium thus produced crystallizes in regular six-sided prisms, with dihedral summits, belonging to the right prismatic system.

Its formula is Mg, NH, PO, +6aq.

It dissolves in 7548 parts of solution of chloride of ammonium, and in 15,627 parts of chloride of ammonium solution containing hydrate of ammonium ; it requires 44,330 parts of water con

taining hydrate of ammonium for its solution ; and it dissolves in 15,293 parts of pure water at the ordinary temperature, but is far more soluble in boiling water, and very readily soluble in most acids.


The special reagents of the first subdivision exert no welldefined action on solutions of magnesium salts.

The special means of recognizing magnesium are these :-its incandescence and blowpipe reaction with nitrate of cobalt (CONO3): its precipitation by carbonate of potassium (K,CO2) in common with the other members of the present subdivision, and the immediate re-solution of this precipitate by the addition of an ammonium salt, while its immediate precipitation from such solutions by the addition of hydrate of ammonium and phosphate of soda is a yet more striking feature. From barium, strontium, and calcium, the excessive solubility of its sulphate will serve to distinguish it; and from calcium it is also distinguished by the immediate solubility of its ferrocyanide in hydrochloric acid.

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We now give a Table exhibiting the general method of distinguishing the members of this subdivision, on the supposition that it is our object to analyse a solution in which only one of these basic radicals exists. It must be borne in mind that this table, like that given on page 81, is meant only to indicate the general plan of procedure in such cases.

Analysis of Subdivision II. The salt may be one of BARIUM, STRONTIUM, CALCIUM, or MAGNESIUM.

Dissolve in water, or in a few drops of hydrochloric acid ; add a considerable quantity of solution of chloride of ammonium ; warm the liquid gently, and add solution of carbonate of ammonium until no more precipitate is produced.

The absence of any! The formation of a precipitate indicates the preprecipitate indicates sence of the presence of

Barium, Strontium, or Calcium. Magnesium, Filter and wash with water; redissolve the preci. which remains in pitate in a few drops of hydrochloric acid, and add

solution as hydrofluosilicic acid with simultaneous agitation. MgCl, NH,Cl. Its presence must be The formation The absence of any precipitate inconfirmed by the of a transparent dicates the presence of addition of a few gelatinous pre Strontium or Calcium. drops of phosphate cipitate indi. Add a solution of ferrocyanide of of sodium, and of cates the pre potassium. hydrate of ammo sence of nium, which will Barium. The formation The absence of a produce a crystalline

of a precipitate, precipitate inprecipitate, either

especially on dicates immediately or after

warming, indi | Strontium, the lapse of a few


the presence of minutes.

Calcium. which must be

confirmed by the addition of a drop of dilute sulphuric

acid, or by the blowpipe flame.



It was remarked in the prefatory observations to the last subdivision, that the present group was distinguished from the

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