proportion of the strong liquid or solid (as purchased) to the water with which it is mixed or in which it is dissolved, the proportion being expressed as a ratio in which the water always stands last; in the case of liquids the numbers express proportion by measure (m.), in the case of solids the proportion by weight (w.). A number is also placed in the fourth column opposite each reagent prepared by dissolving a solid substance, which denotes the weight in grammes of the solid to be dissolved in a Winchester-quart bottle of water.

Thus, No. 2 (524), hydrochloric acid, is prepared by mixing strong HCl with 3 times its measure of distilled water. No. 5, ammonium chloride is made by dissolving solid AmCl in 8 times its weight of water, or by dissolving 300 grammes of solid AmCl in one Winchester-quart of water. Full descriptions are given in paragraphs (511), (514), and (515), of the methods used for making these solutions.

521. The special reagents which stand on shelves above the bench are kept in small bottles, the solids (Nos. 18-21, paragraph 524) in 4 or 6 oz. wide-mouthed stoppered bottles which are filled when necessary from the store jars (stoneware jars with ground clasp-covers),* the liquids (Nos. 117, par. 524) in narrow-necked 4 or 6 oz. bottles supplied from the Winchester-quart bottles in which the store solutions are kept. The general reagents (525, 526) should be kept in bottles of not less than 12 oz. capacity.

522. Labelling.-Bottles intended to contain strong acids or alkalis should have labels etched upon the glass, such bottles are easily purchased; an ordinary paper label, however, protected by paraffin varnish, which is applied according to the directions given below (523), will last for a considerable length of time.

The paper-labels required for reagents and store bottles are most conveniently kept ready gummed in the form of sheets either separate or stitched together into the form of a book. They must be stored in a dry place. They should, as was

* Powdered solids are conveniently removed from large store-jars by means of wooden spoons.

mentioned in (519), bear in bold legible type at least the full name and formula of the substance, the number, if not already printed, being written upon each.* Great care should be bestowed on making the moistened label adhere over its whole surface by gentle pressure with a clean cloth..

523. Varnishing labels.—It is advisable to varnish each label, which is intended to be permanent, as soon as it is perfectly dry; the label is thus protected against being soiled or wetted. The ordinary process consists in first sizing the label by brushing over it a solution of isinglass in water, and then, as soon as this has perfectly dried, applying a thin coat of label varnish; the bottle must not be used until this varnish is quite hard.

A much more simple process of varnishing consists in melting some solid paraffin, which must not be heated so strongly as to cause it to emit vapour, and brushing this rapidly over the dry label with an ordinary varnishing brush; a little practice will soon enable one to apply a uniform film which does not soak into the paper, hardens immediately, and resists the action of water, acids, and alkalis. The chief precaution to be observed is to heat the paraffin as little as possible above its melting point, as, if it is too hot, it greases the paper.

* A book of labels ("A Series of Chemical Labels for use in Laboratories") is sold by Messrs Mottershead, of Manchester, which contains the name of each substance in full, printed in clear type, space being left to insert formula and number.

Messrs Mottershead also supply gummed sheets of labels, printed specially for use with this book, containing all the numbers, names, and formulæ in the lists in pars. 524, 525, 526, 529, 530, 531, and 532.

*

Hydrogen sodium ammonium phosphate (NaAmHPO), solution serves better for

the above for NaHPO4.

Remarks.

[The small numbers refer to corresponding
numbers in the second column.]

1. The strong pure H2SO4 must be poured in the
proper proportion into the water contained in a
large thin beaker or an earthen jar, constantly
stirring the water all the time: the right propor-
tions are obtained by measurement of the height
of the vessel (511). The hot liquid is cooled by
immersing the vessel in cold water, and is then
poured into the store bottle. If the acid is pure,
no white precipitate (PbSO4) forms on dilution.
2. Must be colourless, and give after dilution no
precipitate with either BaCl2 or H2S.

3. Must give no precipitate, after dilution, with
BaCl2 or AgNO3 added to separate portions.

4. Must give no precipitate with BaCl2.

5. Must give no precipitate or coloration with Am S.

6. Must give only a very slight precipitate with lime-water, no coloration with AmS, and separate portions acidified with HNO3 must give no precipitates with BaCl2 and AgNO3. The "Liquor ammoniæ fortissima" is purchased of 880° specific gravity.

7. Must be yellow, and give with acids H2S and a white precipitate of S: it must give no precipitate with solutions of Ca- or Mg-salts.

8. The solid Am2CO3 is dissolved by being heated
with water in a porcelain dish (514): in diluting,
one-fourth of the "Winchester" must be filled
with strong AmHO.

9. Must give no blue precipitate with FeCl solution.
10. Must yield no precipitate with AmHO.
11. The crystallised salt.

12. See (527).

13. Dry, finely-powdered solid. It must, after
having been dissolved in excess of HNO3, give
no precipitate with BaCl2 or AgNO3, or AmйM004
(277), and if evaporated with excess of HCl must
leave no residue insoluble in dilute HCl (290 a).
14. The borax is best dried by heating in a platinum
or porcelain dish until after melting it has again
become solid; this solid mass is then finely pow-
dered in a mortar and kept in a stoppered bottle.
15. In small crystals.

16. Red and blue litmus papers and turmeric paper
in small strips.

precipitation of Mg than does Na,HPO solution: it is prepared of the strength given

525.-REAGENTS FOR GENERAL USE,

Note.-Except in large laboratories it will be unnecessary to keep these contained in the laboratory, may be made up to the right strength as soon as column 4.

* See last column on the preceding page.

AuCl

+ Must be used in very small quantity only, being an expensive reagent.