filter, or else some loss of substance will be incurred; this may be clearly recognised by the filter burning with a carmine red flame. Properties of the precipitate, vide § 46.—The method yields very accurate results in all cases where the addition of alcohol to the solution is admissible; but if we have simply to deal with an aqueous solution, some loss is incurred, since sulphate of strontia is not absolutely insoluble in water; the direct experiments noted sub. No. 50, yielded only 98.12 and 98.02, instead of 100 parts of strontian. This inaccuracy may, however, in a great measure be remedied, by calculating the amount of sulphate of strontia dissolved in the filtrate and the rinsing water, basing this calculation upon the known degree of solubility of sulphate of strontia in acidified and in pure water. Vide Experiment No. 51, which yielded 99.77 instead of 100 parts of strontia.

b. By evaporation.

The same method as described § 74, 1 b.
2. Determination as carbonate of strontia.

a. In solutions.

The same method as described § 74, 2 a.-Properties of the precipitate, vide § 46.-This method yields very accurate results, since carbonate of strontia is nearly absolutely insoluble in water containing ammonia and carbonate of ammonia.-The direct Experiment No. 52 yielded 99.82 instead of 100 parts of

What we stated with regard to barytes (§ 74) applies equally to lime. Fluoride of calcium is, by means of sulphuric acid, converted into sulphate of lime, and the latter, if necessary, is further resolved, by fluxing with carbonated alkali.

Lime is weighed either as sulphate, or as carbonate. (§ 47.)

Of these two methods, that sub. 2 b, is the most frequently applied. This and the method sub. 1 b, yield the most accurate results. The method sub. 1 a, is usually applied only to separate lime from other bases, and that sub. 2 a, generally only in cases where we want to separate lime and other alkaline earths from the alkalies.

1. Determination as sulphate of lime.

a. By precipitation.

Dilute sulphuric acid in excess, is added to the solution of the salt of lime, which it is intended to convert into the sulphate(this is to be done in a beaker-glass); two volumes of alcohol are then added to the mixture, and the whole is allowed to stand at rest for several hours; the fluid is then filtered off from the precipitate, and the latter is washed completely with spirits of wine, dried and ignited. (§ 31.) Properties of the precipitate, vide $47. The results are very accurate. The direct experiment No. 53, yielded 99.64, instead of 100 parts of lime.

b. By evaporation.

The same method as described § 74, 1 b.

2. Determination as carbonate of lime.

The precipitate

b. By precipitation with carbonate of ammonia. The same method as described § 74, 2 a. should be ignited very gently, but the ignition should continue some time. Properties of the precipitate § 47. This method, if properly executed, yields very accurate results; but if the precipitate is washed with pure, instead of ammoniated water, a certain loss of substance is incurred; the direct experiment No. 54, executed in this manner, yielded 99.17, instead of 100 parts of lime. b. By precipitation with oxalate of ammonia.

c. The lime-salt which is to be determined is soluble in water.

The lime salt which it is intended to convert into oxalate of lime, is dissolved in hot water, in a beaker-glass, and oxalate of ammonia added in excess, and moreover, a small portion of ammonia, so as to impart an ammoniacal smell to the fluid, the beakerglass is then covered and placed in a warm spot until the precipitate has completely subsided. The precipitate is then placed upon a filter, in the manner described § 74, 1 a, (sulphate of barytes,)—simply substituting hot water for solution of sal ammoniac. Should it happen that minute particles of the precipitate adhere so firmly to the glass as to resist their removal by mechanical means, they must be dissolved in a few drops of highly dilute hydrochloric acid, and the solution subsequently precipitated with ammonia; this precipitate is to be added to the principal precipitate. After having washed the precipitate carefully, it is to be dried upon the filter in the funnel, and subsequently to be introduced into a platinum crucible; the filter is then incinerated upon the lid of the crucible; the lid with the filter ashes, is placed inverted upon the crucible, and the latter is exposed to a gentle heat, at first, but which is gradually increased until the bottom of the crucible begins to glow faintly; the crucible is kept at this temperature for the space of from ten to fifteen minutes, and subsequently allowed to cool; it is then weighed. If the whole of the process be properly and carefully executed, the results will

prove exceedingly accurate; the direct experiment No. 55 yielded 99.99, instead of 100 parts of lime. To ascertain whether the operation has been perfectly successful, the contents of the crucible, which should appear white and hardly show the slightest inclination to grey, are, after weighing, moistened with some water, and the latter is tested with turmeric-paper. Should the paper turn brown, a sign that the heat applied was too intense, it will be necessary to correct the former operation by throwing a small fragment of pure carbonate of ammonia into the crucible, evaporating to dryness-(best in the water-bath), igniting very gently and weighing the residue; the amount obtained in the second operation will be a trifle higher than that of the first process; the slip of turmeric-paper that has been used as the test, must be washed with water, and the rinsings transferred into the crucible.

For the properties of the precipitate and residue, vide § 47. Many chemists prefer collecting the oxalate of lime upon a weighed filter, to dry at 212°, and to weigh the dry precipitate of oxalate of lime, instead of converting it into the carbonate by ignition. The precipitate obtained in this manner is not, as is often erroneously supposed, Ca O, C, O,, but Ca O, C, O +aq. and ought therefore to be calculated as such. This method is more circumstantial and less accurate in its results than that of converting the oxalate of lime into the carbonate. The direct expe

riment No. 56, yielded 100.45, instead of 100 parts of lime. B. The lime-salt which is to be determined is insoluble in

water.

The salt which it is intended to convert into the oxalate, is dissolved in dilute hydrochloric acid. If the acid is of a nature to escape in this operation, such as carbonic acid, for instance, or of a nature admitting of its removal by evaporation, such as silicic acid, the process is, after the removal of the acid, conducted as described sub. a; but if the acid is of a more stable nature, such as phosphoric acid, for instance, it is necessary first to neutralize the free acid present, with ammonia, until a precipitate begins to form; this precipitate is to be redissolved by the addition of a drop

of hydrochloric acid; oxalate of ammonia in excess is added, and finally acetate of potass; the precipitate formed is allowed to subside, and the further process conducted as sub. a. In this operation the free hydrochloric acid present combines with the potass and ammonia of the acetate and oxalate, liberating a corresponding amount of acetic acid and oxalic acid, in which acids oxalate of lime is nearly insoluble. This method yields very accurate results. In the direct experiment, No. 57, 99.78 parts of lime were obtained, instead of 100 parts.

c. By ignition.

The same method as described § 74, 2 b. The residue remaining upon evaporation with carbonate of ammonia, should be heated very gently. (It is advisable to repeat this operation.)

Many of the compounds of magnesia are soluble in water; those which are insoluble in that menstruum, dissolve in hydrochloric acid, with the exception of silicates.

b. Determination.

Magnesia is weighed either as sulphate or as pyrophosphate, or as pure magnesia.