rides of the alkali metals as directed above. Instead of acetate of baryta, you may also use acetate of lead, removing the excess of lead by sulphuretted hydrogen, and evaporating the filtrate with hydrochloric acid to dryness. Or, you may substitute chloride of lead for the acetate, heat to boiling, and omit the addition of hydrochloric acid in evaporating the filtrate (L. Smith).-Or, you may mix the sulphates with chloride of ammonium in powder, in a crucible, ignite, add a few drops of water and again some chloride of ammonium, ignite once more, and repeat this until the weight remains constant (H. Rose). This latter method I can recommend only where the chlorides contain a comparatively small admixture of sulphate; where this is the case, however, the process is very convenient, as there is no need in it of previously converting the whole mixture into sulphates.

Repeated experiments have shown that the process of separating potassa and soda, as described above, gives always a little less potassa than is really present. If the process is properly conducted, the loss of potassa amounts to about 1 per cent. I have found that it is usually greater in cases where the concentrated solution of the metallic chlorides is mixed with bichloride of platinum, and then with a rather large quantity of alcohol.

b. AMMONIA FROM SODA.

The process is conducted exactly as in a. See also 99, 2. If 3 potassa also is present, the precipitate produced by bichloride of platinum is ammonio-bichloride of platinum+ potassio-bichloride of platinum; in which case the weighed precipitate is cautiously ignited until the chloride of ammonium is expelled (§ 124, b), the residue treated with water, and the chloride of potassium in the solution obtained determined as directed § 97, 3. The weight found is calculated upon potassio-bichloride of platinum, and the result deducted from the weight of the whole precipitate: the difference gives the weight of the ammonio-bichloride of platinum. The s arated platinum may be weighed by way of control.

2. Methods based upon the Volatility of Ammonia and its Salts. AMMONIA FROM SODA AND POTASSA.

a. The salts of the alkalies to be separated contain the same volatile 4 acid, and admit of the total expulsion of their water by drying at 212° F., without losing ammonia (e. g. the metallic chlorides).

Weigh the total mass of the salts in a platinum crucible, and heat, with the lid on, gently at first, but ultimately for some time to faint redness; let the mass cool, and weigh. The decrease of weight gives the quantity of the ammonia salt. If the acid present is sulphuric acid, you must, in the first place, take care to heat very gradually, as otherwise you will suffer loss from the decrepitation of the sulphate of ammonia: and, in the second place, bear in mind that part of the sulphuric acid of the sulphate of ammonia remains with the sulphates of the fixed alkalies, and that you must accordingly convert them into neutral salts, by ignition in an atmosphere of carbonate of ammonia, before proceeding to determine their weight (compare §§ 97 and 98). Chloride of ammonium cannot be separated in this manner from sulphates of the fixed alkalies, as it converts them, upon ignition, partly or totally into chlorides.

b. Some one or other of the conditions given in a is not fulfilled.

If it is impracticable to alter the circumstances by simple means 5 so as to make the method a applicable, the fixed alkalies and the ammonia must be estimated separately in different portions of the compound under examination. The portion in which it is intended to determine the soda and potassa is ignited until the ammonia is completely expelled. The fixed alkalies are converted, according to circumstances, into chlorides or sulphates, and treated as directed § 152, 1. The ammonia is estimated, in another portion, in the manner directed § 99, 3.

3. Indirect Methods.

Of course, a great many of these may be devised; but the follow- 6 ing is the most generally employed.

POTASSA FROM SODA.

Both alkalies are converted into neutral sulphates, or into chlorides (§§ 97 and 98), and weighed in that form; the amount of sulphuric acid or chlorine in them is estimated (see § 132 for sulphuric acid, § 141 for chlorine); and the respective quantities of the soda and potassa are calculated from these data (see below "Calculation of Analyses," $200).

The indirect method of determining potassa and soda is applicable only in the analysis of mixtures containing tolerably large quantities of both bases; but where this is the case, the process answers very well, affording also, more particularly, the advantage of expedition, if the chlorine in the weighed chlorides is determined volumetrically (§ 141, b).

Supplement to the First Group.

SEPARATION OF LITHIA FROM THE OTHER ALKALIES.

Lithia may be separated from potassa and soda in the indirect way, 7 or by either of the following two methods :

a. Treat the chlorides, dried at 248° F., with a mixture of equal volumes of absolute alcohol and anhydrous ether, digest for 24 hours, with occasional shaking, decant on to a filter, and treat the residue again several times with smaller portions of the mixture of alcohol and ether (Rammelsberg, "Pogg. Annal.," 66, 79). Determine, on the one part, the undissolved chloride of potassium and sodium; on the other, the dissolved chloride of lithium, by distilling the fluid off, and converting the chloride of lithium into sulphate. This method is apt to give too much lithium, as chloride of sodium and chloride of potassium are not absolutely insoluble in a mixture of alcohol and ether. The results may be rendered more accurate by treating the impure chloride of lithium, obtained by distilling off the ethereo-alcoholic fluid, once more with the mixture of alcohol and ether, with addition of a drop of hydrochloric acid, adding the residue left to the principal residue, and then only converting the chloride of lithium into sulphate. If the chlorides, which it is intended to treat with alcohol and ether, have been ignited, however so gently, caustic lithia is formed by the action of water, and carbonate of lithia by attraction of carbonic acid; in that case it is necessary,

therefore, to add a few drops of hydrochloric acid, in the process of digestion.

b. Weigh the mixed alkalies, best in form of sulphates, and then 8 determine the lithia or phosphate of lithia according to the directions of § 100. If the quantity of lithia is relatively very small, convert the weighed sulphates into chlorides (2), separate, in the first place, the potassa and soda by means of alcohol, and then determine the lithia (Mayer, "Annal, d. Chem. u. Pharm.," 98, 193). As regards the application of this method, I have to observe that, whilst Mayer asserts that the compound 3 Li O, PO, is actually formed under the circumstances stated in § 100, Rammelsberg ("Pogg. Annal.," 102, 443) still maintains the correctness of his former statement, viz., that the new compound has, indeed, the formula 3 RO, PO,, but contains NaO and Li O in varying proportions; and, in fact, consists perhaps of a combination of 3 Li O, PO, +3 Na O, PO,, mixed with variable proportions of 3 Li O, PO,.

From potassa alone lithia may be separated in the same way as 9 soda, by means of bichloride of platinum. The separation of lithia from ammonia may be effected like that of soda from ammonia,

SECOND GROUP.

BARYTA-STRONTIA-LIME-MAGNESIA.

I. SEPARATION OF THE OXIDES OF THE SECOND GROUP FROM THOSE OF THE FIRST. $153.

Index: Baryta from potassa and soda, 10, 12;-from ammonia, 11. Strontia from potassa and soda, 10, 13;-from ammonia, 11. Lime from potassa and soda, 10, 14;-from ammonia, 11. Magnesia from potassa and soda, 15, 24 ;-from ammonia, 11.

A. General Method.

1. THE WHOLE OF THE ALKALINE EARTHS FROM POTASSA AND 10 SODA.

Principle on which the method is based: Carbonate of ammonia precipitates, from a solution containing chloride of ammonium, only baryta, strontia, and lime.

Mix the solution, in which the bases are assumed to be contained in the form of chlorides, with a sufficient quantity of chloride of ammonium to prevent the precipitation of the magnesia by ammonia; add some ammonia, then carbonate of ammonia in slight excess, let the mixture stand covered for 12 hours in a moderately warm place, filter, and wash the precipitate with water to which a few drops of ammonia have been added.

The precipitate, which contains the baryta, strontia, and lime, is treated as directed in § 154; the filtrate contains the magnesia and the alkalies, and, besides these, exceedingly minute traces of lime, and somewhat more considerable traces of baryta, as the carbonates of these two earths are not absolutely insoluble in a fluid containing chloride of ammonium. In ordinary analyses these minute admixtures may be disregarded; but in cases where a higher degree of accuracy is required, they must be removed. To accomplish this,

add to the filtrate 3 or 4 drops (but not much more) of dilute sulphuric acid, then a few drops of oxalate of ammonia, and let the fluid stand again for 12 hours in a warm place. If a precipitate forms, collect this on a small filter, wash, and treat on the filter with some dilute hydrochloric acid, which dissolves the oxalate of lime, and leaves the sulphate of baryta undissolved.

Evaporate the filtrate, which contains the magnesia and the alkalies, according to circumstances, either at once, or after previous removal of the traces of lime and baryta, to dryness, and remove the ammonia salts by gentle ignition in a covered crucible, or in a small covered dish of platinum or porcelain.* In the residue, separate the magnesia from the alkalies by one of the methods given in § 153, B, 4 (15-24).

2. THE WHOLE OF THE ALKALINE EARTHS FROM AMMONIA.-The 11 same principle and the same process as in the separation of potassa and soda from ammonia (see § 152).

B. Special Methods.

SINGLE ALKALINE EARTHS FROM POTASSA AND SODA.

1. BARYTA FROM POTASSA AND SODA.

Precipitate the baryta with dilute sulphuric acid (§ 101, 1, a), 12 evaporate the filtrate to dryness, and ignite the residue, with addition of carbonate of ammonia (§ 97, 1-98, 1). Take care to add a sufficient quantity of sulphuric acid to convert the alkalies also completely into sulphates.

This method is, on account of its greater accuracy, preferable to the one in A, in cases where the baryta has to be separated only from one of the two fixed alkalies; but if both alkalies are present, the other method is more convenient, since the alkalies are obtained in it as chlorides.

2. STRONTIA FROM POTASSA AND SODA.

Strontia may be separated from the alkalies, like baryta, by means 13 of sulphuric acid; but this method (precipitation of the strontia as sulphate) is not preferable to the one in A (10), in cases where the choice is permitted (compare § 102).

3. LIME FROM POTASSA AND SODA.

Precipitate the lime with oxalate of ammonia (§ 103, 2, b, a), filter, 14 evaporate the filtrate to dryness, and determine the alkalies in the ignited residue. In determining the alkalies, dissolve the residue, freed by ignition from the ammonia salts, in water, and filter the solution from the undissolved portion; acidify the filtrate, according to circumstances, with hydrochloric acid or sulphuric acid, and then evaporate to dryness; since oxalate of ammonia partially decomposes chlorides of the alkali metals upon ignition, and converts the bases into carbonates, except in presence of a large proportion of chloride of ammonium. The results are still more accurate than in A, ex

• This operation effects also the removal of the small quantity of sulphuric acid added to precipitate the traces of baryta, as sulphates of the alkalies are converted into chlorides of the alkali metals upon ignition in presence of a large proportion of chloride of ammonium.

cept where oxalate of ammonia has been used, after the precipitation by carbonate of ammonia, to remove the minute traces of lime from the filtrate.

4. MAGNESIA FROM POTASSA AND SODA.

a. Methods based upon the sparing solubility of Magnesia in Water. a. Make a solution of the bases, as neutral as possible, and free 15 from ammonia salts (whether the acid is sulphuric acid, hydrochloric acid, or nitric acid, is indifferent), add baryta-water as long as a precipitate forms, heat to boiling, filter the fluid off from the precipitate, and wash the latter with boiling water. The precipitate contains the magnesia as hydrate; the magnesia is determined either as directed in § 104, 1, b, or the precipitate is dissolved in hydrochloric acid, the baryta thrown down with sulphuric acid, and the magnesia as phosphate of magnesia and ammonia (104, 2). The alkalies, which are contained in the solution, according to circumstances, as chlorides, nitrates, or caustic alkalies, are separated from the baryta as directed in 10 or 12. Liebig, who was the first to employ this method, proposes crystallized sulphide of barium as precipitant. The method gives good results, but is rather tedious.

3. Precipitate the solution with a little pure milk of lime, boil, 16 filter, and wash. Separate the lime and the magnesia in the precipitate as directed § 154; the lime and the alkalies in the filtrate, as directed in 10 or 14. This method is advantageously employed in cases where it is desirable to remove the magnesia from a fluid containing lime and alkalies, which latter alone it is intended to determine.

7. Evaporate the solution of the chlorides (which must contain no 17 other acids) to dryness, and, if chloride of ammonium is present, ignite; warm the residue with a little water; this will dissolve it with the exception of some magnesia, which separates. Add to the solution elutriated oxide of mercury, evaporate to dryness on the water-bath, with frequent stirring, and proceed exactly as directed § 104, 3, b. There is no need to continue the ignition until the whole of the oxide of mercury is expelled; on the contrary, part of it may be filtered off together with the magnesia, and subsequently volatilized upon the ignition of the latter. The solution contains the alkalies in form of chlorides (Berzelius). This method gives satisfactory results. Take care to add the oxide of mercury only in proper quantity, and always test the solution of the alkaline chlorides for magnesia, of which it will generally be found to retain a trace.

d. Add to the solution of the chlorides oxalic acid in sufficient 18 quantity to convert all the bases present, viewed as potassa, into quadroxalate; add some water, evaporate to dryness, in a platinum dish, and ignite.

By this operation the chlorides of the alkali metals are partially, the chloride of magnesium completely, converted into oxalates, which, upon ignition, give carbonated alkalies and magnesia. The salts of the alkalies are separated from the magnesia by boiling water. If the solution looks a little turbid, evaporate to dryness, treat the residue with water, and filter off the trifling amount of magnesia still remaining; add, finally, hydrochloric acid to the filtrate, and determine the alkalies as chlorides.