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lake has a bright orange colour, and is chiefly used by calicoprinters.

Orange-Lake.-lb. of fustic extract is dissolved in water, and lb. of lead acetate added thereto.

Orange-Lake.-Precipitate a mixture of fustic extract and annatto dissolved in a little carbonate of soda with alum and tin crystals.

MADDER-LAKES.-These are largely used by artists on account of the brilliancy of their tint and superior permanency over other lakes. Several methods have been published for their preparation.

(a) Englefield's Process.-Tie 2 oz. of madder in a piece of thin cloth, and beat it well in 1 pint of water in a stone mortar, and repeat the process with 5 successive pints of fresh water, until the material ceases to yield colour; the mixed liquors are boiled in an earthen vessel, and 1 oz. of alum is dissolved in the pint of water, then a solution of oz. of potassium carbonate is slowly added, and the mixture allowed to stand until cold; the top liquor is decanted off, and the lake well washed in hot water, filtered, and dried.

(b) Macerate 2 lbs. of ground madder in 1 gallon of water for 10 to 15 minutes, and repeat the process with 2 or 3 successive quantities of water; the liquors are mixed and lb. of alum is added; the mixture is gently heated nearly to the boiling point for 3 or 4 hours, filtered, and a solution of sodium carbonate added as long as a precipitate falls; this is filtered, well washed with water, and dried.

(c) 2 lbs. of madder are steeped in tepid water for 26 hours, and a slight fermentation set up, whereby the decomposition of the glucoside of the madder is effected, which means an increase in the colouring power of the extract; to the mass is now added a solution of 2 lbs. of alum, the mixture being maintained at about 150° F. from 3 to 6 hours, when the liquor is strained and precipitated with sodium carbonate as long as a precipitate falls down; the precipitate is filtered, washed, and dried as usual.

(d) Add to the decoction of madder a small quantity of acetate of lead solution, which throws down a brown colouring matter which is present in the dyestuff; after filtering this off, the clear liquor is treated with alum and tin as usual.

(e) Garancine is a more or less purified madder, the useless glucoside (or ruberythric acid) of which has been converted into useful colouring matter, and may be used in the preparation of madder lakes. The process is to treat 1 lb. of the garancine with successive portions of a boiling solution of lb. of alum

in 2 gallons of water, using altogether about 2 gallons; after extraction, the liquor is filtered, and allowed to cool, when the colouring matter separates out as a flocculent precipitate; this is collected and dissolved in ammonia, and to the solution is added alum, or a mixture of alum and tin chloride, sufficient to precipitate the colouring matter. The depth of colour of the lake depends upon the amount of alum used, provided there be sufficient ammonia to precipitate all the alum added; the more alum the paler the tint of the lake.

(f) Persoz Process.-1 lb. of garancine, and 1 lb. of sodium sulphate are boiled together in 18 pints of water; to the mixture is added 1 lb. of alum, previously dissolved in water, and the mass allowed to stand for some time for the alum to extract the colouring principle of the garancine; the mass is next strained, and to the clear liquor is added 1 lb. of lead acetate; lead sulphate is precipitated, and this is filtered off; on boiling the clear filtrate the lake formed is collected, washed, and dried.

MADDER RED LAKES.—(a) By combining both madder and cochineal bright carmine-red lakes can be prepared. A decoction of madder and alum is prepared in the manner described above under madder lakes (c); to this is added an ammoniacal solution of cochineal (prepared by digesting 1 lb. of cochineal in 4 ozs. of ammonia diluted with its own volume of water for a few days) as long as a precipitate falls down. This is collected, washed, and dried.

(b) A cheap red lake can be made by mixing decoctions of madder and Brazil wood, adding carbonate of soda, and precipitating with alum, or alum and tin, in the usual way. The recipes for preparing madder and Brazil wood lakes may be combined to produce the compound lake.

Madder only contains the colouring principle, alizarine, in comparatively small proportion; with it is associated other colouring matters and impurities, which, as a rule, are more soluble in boiling than in cold water; hence it is necessary to avoid extracting madder with boiling water, otherwise these impurities pass into the extract and injuriously affect the tint of the resulting lake. The bulk of the colouring matter exists in the madder in the form of a glucoside named ruberythric acid; this, by fermentation, is converted into the colouring principle, alizarine. It is well to take advantage of this in the process of preparing madder lake by steeping the madder in a little tepid water for a day or so, and then extracting the colouring principle with alum as described under method (c) above.

Madder lakes, when pure, are fairly bright in tint, and good as

regards both their covering and colouring powers. They are almost entirely soluble in solutions of caustic potash or caustic soda, but not in weak ammonia, which character serves as a distinguishing point from carmine. Boiled with dilute sulphuric or hydrochloric acid madder lakes are decomposed, alizarine, the colouring principle of the madder, being liberated as a brownishyellow precipitate. When used as pigments they are more permanent than other lakes; in dry air they are nearly permanent, but in moist air they fade a little.

GREEN LAKES.-Chinese green and sap green are similar to lakes in composition and properties; they have already been described. There are no other green pigments prepared from vegetable dyestuffs by precipitation as lakes; most of what are sold as green lakes are either lakes made from coal-tar colours (as described below) or with mixtures of either Prussian blue or indigo and gamboge, not true lakes.

VIOLET LAKE.—(1) A violet lake can be made by adding 2 gallons of antimony chloride, at 52° Tw., to each 16 gallons of a decoction of logwood (10° Tw.). The lake is immediately precipitated, and is filtered, washed, and dried.

(2) 3 lbs. of alum are dissolved in 1 gallon of water, and to the solution is added 21⁄2 lbs. of lead acetate previously dissolved in a little water; the precipitated sulphate of lead is filtered off and the clear liquor is used in preparing the lake. 6 lbs. of logwood are made into a decoction with 10 gallons of water, and to 10 gallons of this liquor 1 gallon of lead-alum liquor is added; the lake precipitated is collected, washed, and dried. It has a fine violet colour, but is not fast.

The lake colours are often sold in the form of pastes for the purpose of colouring beverages, sweets, &c. The author has had occasion to make analyses from time to time of such pigments, and the following are selections from such analyses :—

ANALYSES OF LAKE COLOURS.

1. 2. 3. 4. 5. 6. Water, 80.40 80.00 79.45 68.2 79.45 82.0 Ash, 6.75 9.55 10.20 19.9 10.60 9.3 Colouring matter, 12.85 10.45 10.35 11.9 9.95 8.7

7.

88.75

3:00 8.25

100.00 100.00 100.00 100.0 100.00 100.0 100.00

1. Scarlet from Lima wood with alumina.

2. Orange-scarlet from peach wood with alumina.

3. A brownish-yellow from Persian berries with alumina.
4. Olive-yellow from Persian berries with lead and chalk.

5. Orange made from fustic and annatto with alum and tin.

6. Violet-brown from Lima wood with alum, lead, and iron.
7. Blue-black from logwood and iron.

General Considerations on Lake-making.-The preparation of lakes is a matter of some difficulty, especially when it is desired to prepare successive batches, perhaps at some considerable interval of time, of the same depth and brilliance of colour. This difficulty arises almost entirely from the variable character of the dyestuffs or colouring matter used, the natural colouring matters varying considerably in actual colouring power; this makes it impossible for the users, either lake-makers or dyers, to always work from very definite recipes; these must be modified from time to time, according to the actual strength of the batch which is being used. If the colouring power of the dyestuff is weak, then more must be used to produce a lake of a given shade than if the colouring power is either normal or above the average; or, if no more dyestuff is used, then the proportion of base must be varied to suit the strength or colouring power of the dyestuff.

The depth of tint or colour of the lake which is prepared depends, as may naturally be inferred, on the proportions of the base or precipitating agent to the colouring matter; the greater the proportion of base the paler will be the tint of the lake produced. As the preparation of lakes is a chemical operation depending upon the combination of the colouring principle of the dyestuff with the base (alumina, tin, &c.), there will be a definite relationship between the two bodies, resulting in the formation of a lake having the maximum depth of colour. What these proportions are has not yet been determined; they necessarily vary with different colouring matters, and even with different batches of the same colouring matters. Any excess of dyestuff used over these proportions does not lead to any increase in the depth of the lake formed, but such excess is left unused, and may probably be thrown away; on the other hand, any excess of base reduces the tint of the lake, as has been explained above.

After precipitation, the lake should be well washed, and dried slowly at as low a temperature as possible. Usually lakes are made up in the form of conical masses, drops, or troches; this is done by mixing a small quantity of gum or glue water with the wet lake, then pressing the mass into moulds, or moulding between the fingers, then drying in the usual way.

The following description of the reactions given by various chemical reagents with decoctions of the principal natural dyestuffs used in lake-making may be found of use, especially in the examination of lakes for the purpose of ascertaining how they are made; but it may be pointed out that it will always be advisable for the analyst to make such experiments on his own

account, for the purpose of observing the exact shade of colorations produced, as it is impossible to convey, with sufficient exactitude, an idea of the actual tint of any coloration or precipitate which may be produced.

Cochineal.-Alumina sulphate gives a bright crimson solution; on the addition of sodium or potassium carbonate a crimson precipitate falls down. Stannous chloride gives a dull purplish coloured precipitate; copper sulphate a purple precipitate; ferric chloride a brown precipitate; caustic soda a bluish crimson solution. Strong sulphuric acid changes the colour of the decoction to an amber colour, and, on adding water, a pale yellow solution is obtained.

Brazil Wood.-Alumina sulphate gives a red precipitate. Stannous chloride throws down a pale crimson precipitate; lead acetate a violet-rose precipitate; ferric chloride a chocolatebrown precipitate; copper sulphate a brick-red precipitate; and caustic soda forms a crimson solution. Strong sulphuric acid changes the colour of the decoction to a red-brown, and on diluting this with water a pale amber solution is obtained.

Persian Berry.-Alumina sulphate has no action. On further adding ammonia or caustic soda, a brownish-olive precipitate falls down, while alkaline carbonates throw down a brighter yellow precipitate. Stannous chloride throws down an olive-yellow precipitate, lead acetate a yellow-brown precipitate, and ferric chloride a dark olive-green precipitate. Nitric acid forms a red solution. Strong sulphuric acid forms a yellowbrown solution, and on adding water a brown precipitate falls down.

Quercitron.-Alumina sulphate throws down an ochreyellow precipitate, stannous chloride an orange-yellow precipitate, lead acetate a dark yellow-brown precipitate, copper sulphate a brownish-olive precipitate, and ferric chloride a dark olive-green precipitate. Caustic soda forms a dark yellowbrown solution, from which acids throw down a yellow-brown precipitate. Strong sulphuric acid forms a brownish-yellow solution, from which, on adding water, a dark brown precipitate falls down.

Fustic.-Alumina sulphate, stannous chloride and lead acetate throw down orange-yellow precipitates; the first is bright, the last rather duller than those with the other two salts. Copper sulphate throws down a dull yellow precipitate, and ferric chloride a dark olive-brown precipitate. Strong sulphuric acid forms a brown-yellow solution, from which, on diluting with water, a brown precipitate falls down.

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