acetic acid, even if boiling, nor any appreciable trace of it, to boiling nitric acid, though the solution had contained that salt.*

b. By Evaporation.

Add to the solution, in a weighed platinum dish, pure sulphuric acid very slightly in excess, and evaporate on the water-bath; expel the excess of sulphuric acid by cautious application of heat, and ignite the residue. For the properties of sulphate of baryta, see § 71.

Both methods, if properly and carefully executed, give almost absolutely accurate results.

2. Determination as Carbonate of Baryta.

a. In Solutions.

Mix the moderately dilute solution of the baryta salt, in a beaker with ammonia, add carbonate of ammonia in moderate excess, and let the mixture stand several hours in a warm place. Filter, wash the precipitate with water mixed with a little ammonia, dry, and ignite ($ 53).

For the properties of the precipitate, see § 71. This method involves a trifling loss of substance, as the carbonate of baryta is not absolutely insoluble in water. The direct experiment, No. 57, gave 99-79 instead of 100 parts of baryta.

If the solution contains a notable quantity of ammoniacal salts, the loss incurred is much more considerable, since the presence of such salts greatly increases the solubility of the carbonate of baryta.

b. In Salts of Baryta with Organic Acids.

Heat the salt slowly in a covered platinum crucible, until no more fumes are evolved; place the crucible obliquely, with the lid leaning against it, and heat to redness, until the whole of the carbon is consumed, and the residue presents a perfectly white appearance; moisten the residue with a concentrated solution of carbonate of ammonia, evaporate, ignite gently, and weigh. The results obtained by this method are quite satisfactory. A direct experiment, No. 58, gave 99.61 instead of 100 parts of baryta. The loss of substance, which almost invariably attends this method, is owing to particles of the salt being carried away with the fumes evolved upon ignition, and is accordingly the less considerable, the more slowly and gradually the heat is increased. Omission of the moistening the residue with carbonate of ammonia would involve a further loss of substance, as the ignition of carbonate of baryta in contact with carbon is attended with formation of some caustic baryta, and evolution of carbonic oxide gas.

a. Solution.

§ 102.

2. STRONTIA.

See the preceding paragraph (§ 101, a.-Solution of baryta), the directions there given applying equally here.

b. Determination.

Strontia is weighed either as sulphate or as carbonate of strontia (§ 72). Strontia in the pure state, or in form of carbonate, may be determined also by the volumetrical (alkalimetrical) method.Co mp. § 223.

* I mention this in reference to Siegle's statement in the "Journal f. prakt. Chem.," 69, 142, that acetic acid and nitric acid will still extract small quantities of chloride of barium from sulphate of baryta, formed in presence of an excess of sulphuric acid, and thoroughly washed with water.

b. By Evaporation.

All salts of strontia with volatile acids, if no other non-volatile body is present.

2. CARBONATE OF STRONTIA.

a. All compounds of strontia soluble in water.

B. Salts of strontia with organic acids.

The method based on the precipitation of strontia with sulphuric acid yields accurate results only in cases where the fluid from which the strontia is to be precipitated may be mixed, without injury, with alcohol. Where this cannot be done, and where the method based on the evaporation of the solution of strontia with sulphuric acid is equally inapplicable, the conversion into the carbonate ought to be resorted to in preference, if admissible, in the case of soluble compounds of strontia and of salts of strontia with organic acids.

1. Determination as Sulphate of Strontia.

a. By Precipitation.

Mix the solution of the salt of strontia (which must not be too dilute, nor contain much free hydrochloric or nitric acid), with dilute sulphuric acid in excess, in a beaker, and add, at least, an equal volume of alcohol; let the mixture stand a few hours, and filter; wash the precipitate with dilute spirit of wine, dry, ignite, and weigh the residue (§ 53).

If the circumstances of the case contraindicate the use of alcohol, the fluid must be precipitated in a tolerably concentrated state, allowed to stand in the cold for at least twenty-four hours, filtered, and the precipitate washed with cold water, until the last rinsings manifest no longer an acid reaction, and leave no perceptible residue upon evaporation. If traces of free sulphuric acid remain adhering to the filter, the latter turns black on drying, and crumbles to pieces; too long protracted washing of the precipitate, on the other hand, tends to increase the loss of substance inseparable from the application of this method in cases where the use of alcohol is inadmissible.

Care must be taken that the precipitate be thoroughly dry, before proceeding to ignite it; otherwise it will be apt to throw off fine particles during the latter process. The filter, which is to be burnt on the lid of the crucible, must be as clean as possible, or some loss of substance will be incurred; as may be clearly seen from the depth of the carmine tint of the flame with which the filter burns if the precipitate has not been properly removed.

For the properties of the precipitate, see § 72. This method gives very accurate results in cases where the addition of alcohol to the solution is admissible; but where we have to deal with a simple aqueous solution, a rather considerable loss is unavoidable, as sulphate of strontia is not absolutely insoluble in water. The direct experiments, No. 59, gave only 98.12 and 98-02 instead of 100 parts of strontia. However, the error may, in a great measure, be rectified, by calculating the amount of sulphate of strontia dissolved in the filtrate and the rinsing water, basing the calculation upon the known degree of solubility of sul

phate of strontia in pure and acidified water. See Experiment No. 60, which, with this correction, gave 99.77 instead of 100 parts of

The same method as described § 101, 2, a. For the properties of the precipitate, see § 72. The method gives very accurate results, as carbonate of strontia is nearly absolutely insoluble in water containing ammonia and carbonate of ammonia. A direct experiment, No. 60, gave 99.82 instead of 100 parts of strontia. Presence of ammoniacal salts exercises here a less adverse influence, than in the precipitation of carbonate of baryta.

b. In Salts with Organic Matter.

The same method as described § 101, 2, b. The remarks made there, respecting the accuracy of the results, apply equally here.

a. Solution.

§ 103.

3. LIME.

See § 101 a.-Solution of baryta. Fluoride of calcium is, by means of sulphuric acid, converted into sulphate of lime, and the latter again, if necessary, decomposed by boiling or fluxing with an alkaline carbonate (§ 132).

b. Determination.

Lime is weighed either as sulphate, or as carbonate of lime (§ 73). Small quantities of lime are also occasionally reduced to the caustic state, instead of being converted into carbonate. Lime in the pure state, or in form of carbonate, may be determined also by the volumetrical (alkalimetrical) method. Comp. § 223.

We may convert into

1. SULPHATE OF LIME.

a. By Precipitation.

All salts of lime with acids soluble in alcohol, provided no other substance insoluble in alcohol be present.

b. By Evaporation.

All salts of lime with volatile acids, provided no non-volatile body be present.

2. CARBONATE OF LIME.

a. By Precipitation with Carbonate of Ammonia.

All salts of lime soluble in water.

b. By Precipitation with Oxalate of Ammonia. All salts of lime soluble in water or in hydrochloric acid.

c. By Ignition.

Salts of lime with organic acids.

Of these several methods, 2, b. (precipitation with oxalate of ammonia) is the one most frequently resorted to. This, and the method 1, b, give the most accurate results. The method, 1, a, is usually resorted to only

to effect the separation of lime from other bases; 2, a, generally only to effect the separation of lime together with other alkaline earths from the alkalies.

1. Determination as Sulphate of Lime.

a. By Precipitation.

Mix the solution of lime in a beaker, with dilute sulphuric acid in excess, and add twice the volume of alcohol; let the mixture stand twelve hours, filter, and thoroughly wash the precipitate with spirit of wine, dry, and ignite moderately (§ 53). For the properties of the precipitate, see § 73. The results are very accurate. A direct experiment, No. 62, gave 99.64 instead of 100 parts of lime.

b. By Evaporation.

The same method as described § 101, 1, b. See also § 103, 2, b, a. 2. Determination as Carbonate of Lime.

a. By Precipitation with Carbonate of Ammonia.

The same method as described § 101, 2, a. The precipitate must be exposed only to a very gentle red heat, but this must be continued for some time. For the properties of the precipitate, see § 73.

This method gives very accurate results, the loss of substance incurred being hardly worth mentioning.

If the solution contains chloride of ammonium or similar ammoniacal salts in considerable proportion, the loss of substance incurred is far greater. The same is the case if the precipitate is washed with pure instead of ammoniacal water. A direct experiment, No. 63, in which pure water was used, gave 99·17 instead of 100 parts of lime.

b. By Precipitation with Oxalate of Ammonia.

a. The Lime Salt is soluble in Water.

Dissolve the salt in hot water, in a beaker; add oxalate of ammonia in moderate excess, and then ammonia sufficient to impart an ammoniacal smell to the fluid; cover the glass, and let it stand in a warm place until the precipitate has completely subsided, which will require twelve hours, at least. Pour the clear fluid gently and cautiously, so as to leave the precipitate undisturbed, on a proper filter. As soon as the fluid has passed through, transfer the precipitate also to the filter, by rinsing with hot water, taking care, after the addition of every fresh portion, to wait until the fluid has completely passed through the filter. Small particles of the precipitate, adhering more firmly to the glass, are removed with a feather. If this fails to effect their complete removal, they should be dissolved, in a small vessel, in a few drops of highly dilute hydrochloric acid, ammonia added to the solution, and the oxalate obtained added to the first precipitate. Deviations from the rules laid down here will generally give rise to the passing of a turbid fluid through the filter. After having washed the precipitate, dry it on the filter in the funnel, and transfer the dry precipitate to a platinum crucible, taking care to scrape the filter as clean as practicable; burn the filter on a piece of platinum wire, letting the ash drop into the hollow of the lid; pat the latter, now inverted, on the crucible, to prevent the filter ash mixing with the precipitate; apply a gentle heat, and increase this gradually, until the bottom of the crucible is heated to very faint redness. Keep it at that temperature from ten to fifteen minutes, then let it cool,

and weigh. After this, moisten the contents of the crucible, which must be perfectly white, or barely show the least tinge of gray, with a little water, and test this after a time with a slip of turmeric paper. If the color of the test paper remains unaltered, the process may be considered at an end, and the result taken as correct; but should the paper turn brown-a sign that the heat applied was too inteuse -rinse off the fluid adhering to the paper with a little water into a crucible, throw in a small lump of pure carbonate of ammonia, evaporate to dryness (best in the water-bath), heat to very faint redness, and weigh the residue. If the weight shows an increase over that of the first residue, repeat the same operation until the weight remains constant. This method, if properly and carefully performed, in strict accordance with the directions, gives nearly absolutely accurate results; and if the application of heat is properly managed, there is no need of the tedious supplementary operation recommended here-evaporation with carbonate of ammonia. A direct experiment, No. 67, gave 99.99 instead of 100 parts of lime.

For the properties of the precipitate and residue, see § 73.

If the quantity of oxalate of lime obtained is only very trifling, I prefer to convert it into the sulphate, or to reduce it to the caustic state. To effect the latter, the oxalate of lime is heated to intense redness, in a small platinum crucible, over a gas blowpipe-flame, and the operation continued long enough to effect the reduction of the oxalate to the caustic state. The conversion of the oxalate into sulphate is effected most conveniently by Schrötter's method, viz., ignition with pure sulphate of ammonia.

Many chemists prefer collecting the oxalate of lime upon a weighed filter, drying at 212° F., and weighing the dry precipitate. This precipitate is not, as is often erroneously supposed, Ca Ó, CO̟, but, Ca O, C,O,+ aq., and must therefore be calculated as such.

This method, besides being more tedious, gives less accurate results than that based on the conversion of the oxalate into the carbonate. The direct experiment, No. 65, gave 100-45 instead of 100 parts of lime. Instead of weighing the oxalate of lime as such, or in form of carbonate, &c., the quantity of lime present in the salt may be determined also by two different volumetrical methods.

a. Ignite the oxalate, converting it thus into a mixture of carbonate and caustic lime, and determine the quantity of the lime by the alkalimetrical method described in § 223; or,

b. Determine the oxalic acid in the well-washed but not yet dried oxalate of lime, by means of permanganate of potassa (§ 137), and reckon for each equivalent of oxalic acid (C, O,) an equivalent of lime (Hempel).

With proper care, both these volumetrical methods give as accurate results as those obtained by weighing. (Comp. Experiment No. 66.) They deserve to be recommended more particularly in cases where an entire series of quantitative estimations of lime has to be made. Under certain circumstances it may also prove advantageous to precipitate the lime with a measured quantity of a standard solution of oxalic acid or quadraoxalate of potassa, filter, and determine the excess of oxalic acid in the filtrate (Kraut. "Chem. Centralbiatt," 1856, 316).

B. The Salt is insoluble in Water.

Dissolve the salt in dilute hydrochloric acid. If the acid combined with the lime is of a nature to escape in this operation (e. g.,