Alexander Watt

USEFUL NOTES AND TABLES.

Preparation of Lakes.—Brazil-wood Lake.—Cochineal Lake.—Lac Lake.—Madder Lake.—Orange Lake.—Yellow Lake.—Artificial Ultramarine.—Twaddell's Hydrometer.—Dalton's Table showing the proportion of Dry Soda in Leys of Different Densities.—Table of Strength of Caustic Soda Solutions at 59° F.—Table showing the Specific Gravity corresponding with the degrees of BaumÉ's Hydrometer.—Table of Boiling Points of Alkaline Leys.—Table showing the Quantity of Caustic Soda in Leys of Different Densities.—Table showing the Quantity of Bleaching Liquid at 6° Twaddell required to be added to Weaker Liquor to raise it to the given Strength.—Comparative French and English Thermometer Scales.—Weights and Measures of the Metrical System.—Table of French Weights and Measures.—List of Works relating to Paper Manufacture.

Preparation of Lakes.—These are prepared by either of the following processes:—1. By adding a solution of alum, either alone or partly saturated with carbonate of potassa, to a filtered infusion or decoction of the colouring substance, and after agitation precipitating the mixture with a solution of carbonate of potash ("salt of tartar"). 2. By precipitating a decoction or infusion of the colouring substance made with a weak alkaline ley, by adding a solution of alum. 3. By agitating recently precipitated alumina with a solution of the colouring matter, prepared as before, until the liquid is nearly discoloured, or the alumina acquires a sufficiently dark tint. The first method is usually employed for aciduous solutions of colouring matter, or for those whose tint is injured by alkalies; the second for those that are brightened, or at least uninjured, by alkalies; the third, those colouring matters that have a great affinity for gelatinous alumina, and readily combine with it by mere agitation. By attention to these general rules, lakes may be prepared from almost all animal and vegetable colouring substances that yield their colour to water, many of which will be found to possess great beauty and permanence.

The precise process adapted to each particular substance may be easily ascertained by taking a few drops of its infusion or decoction, and observing the effects of alkalies and acids on the colour.

The quantity of alum or of alumina employed should be nearly sufficient to decolour the dye-liquor, and the quantity of carbonate of potassa should be so proportioned to the alum as to exactly precipitate the alumina, without leaving free or carbonated alkali in the liquid. The first portion of the precipitate has the deepest colour, and the shade gradually becomes paler as the operation proceeds.

A beautiful "tone" of violet, red, and even purple may be communicated to the colouring matter of cochineal by the addition of perchloride of tin; the addition of arseniate of potassa (neutral arsenical salt) in like manner gives shades which may be sought for in vain with alum or alumina. After the lake is precipitated it must be carefully collected, washed with cold distilled water, or the purest rain-water, until it ceases to give out colour.

Brazil-wood Lake.—1. Take of ground Brazil wood 1 lb., water 4 gallons; digest for 24 hours, then boil for 30 or 40 minutes, and add of alum 1½ lb., dissolved in a little water; mix, decant, strain, and add of solution of tin ½ lb.; again mix well and filter; to the clear liquid add, cautiously, a solution of salt of tartar or carbonate of soda, as long as a deep-coloured precipitate forms, carefully avoiding excess. 2. Add washed and recently precipitated alumina to a strong and filtered decoction of Brazil wood. Inferior to the last.

Cochineal Lake.—1. Cochineal (in coarse powder) 1 oz.; water and rectified spirit, of each, 2½ ozs.; digest for a week; filter and precipitate the tincture with a few drops of solution of tin, added every 2 hours, until the whole of the colouring matter is thrown down; lastly, wash the precipitate in distilled water and dry it; very fine. 2. Digest powdered cochineal in ammonia water for a week, dilute the solution with a little water, and add the liquid to a solution of alum, as long as a precipitate falls, which is the lake. Equal to the last. 3. Coarsely powdered cochineal 1 lb., water 2 gallons; boil 1 hour, decant, strain, add a solution of salt of tartar, 1 lb., and precipitate with a solution of alum. By adding the alum first, and precipitating the lake with the alkali, the colour will be slightly varied. All the above are sold as carminated or Florence lake, to which they are often superior.

Lac Lake.—Boil fresh stick-lac in a solution of carbonate of soda, filter the solution, precipitate with a solution of alum, and proceed as before. A fine red.

Madder Lake.—1. Take of Dutch grappe or crop madder 2 oz., tie it in a cloth, beat it well in a pint of water in a stone mortar, and repeat the process with fresh water (about 5 pints) until it ceases to yield colour; next boil the mixed liquor in an earthen vessel, pour it into a large basin, and add of alum 1 oz., previously dissolved in boiling water, 1 pint; stir well, and while stirring, pour in gradually of a strong solution of carbonate of potassa (salt of tartar) 1½ oz.: let the whole stand until cold, then pour off the supernatant liquor, drain, agitate the residue with boiling water, 1 quart (in separate portions), decant, drain, and dry. Product, ½ oz. The Society of Arts voted their gold medal to the author of the above formula. 2. Add a little solution of acetate of lead to a decoction of madder, to throw down the brown colouring matter, filter, add a solution of tin or alum, precipitate with a solution of carbonate of soda or of potassa, and otherwise proceed as before. 3. Ground madder, 2 lbs.; water, 1 gallon; macerate with agitation for 10 minutes, strain off the water, and press the remainder quite dry; repeat the process a second and a third time; then add to the mixed liquors, alum, ½ lb., dissolved in water, 3 quarts; and heat in a water-bath for 3 or 4 hours, adding water as it evaporates: next filter, first through flannel, and when sufficiently cold, through paper; then add a solution of carbonate of potassa as long as a precipitate falls, which must be washed until the water comes off colourless, and lastly, dry. If the alkali be added in 3 successive doses, 3 different lakes will be obtained, successively diminishing in beauty.

Orange Lake.—Take of the best Spanish annotta 4 ozs.; pearlash, ¾ lb.; water, 1 gallon; boil it for half an hour, strain, precipitate with alum, 1 lb., dissolved in water, 1 gallon, observing not to add the latter solution when it ceases to produce an effervescence or a precipitate. The addition of some solution of tin turns this lake a lemon yellow; acids redden it.

Yellow Lake.—1. Boil French berries, quercitron bark, or turmeric, 1 lb., and salt of tartar, 1 oz., in water, 1 gallon, until reduced to one half; then strain the decoction and precipitate with a solution of alum. 2. Boil 1 lb. of the dye-stuff with alum, ½ lb.; water, 1 gallon, as before, and precipitate the decoction with a solution of carbonate of potash.

Artificial Ultramarine.—This is obtained by several processes, of which the following are examples:—1. Take kaolin, 37 parts; sulphate of soda, 15; carbonate of soda, 22; sulphur, 18; and charcoal, 8 parts; mix these intimately, and heat in large covered crucibles for twenty-four to thirty hours. The resulting product is then to be again heated in cast-iron boxes at a moderate temperature, until the required tint is obtained; it is finally pulverised, washed in a large quantity of water, and the floating particles allowed to subside in a separate vessel; the deposited colour is now collected and dried. 2. Expose to a low red heat, in a covered crucible as long as fumes are given off, a mixture composed of: kaolin, 2 parts; anhydrous carbonate of soda and sulphur, of each 3 parts. Some persons use one-third less carbonate of soda.

Twaddell's Hydrometer, which is much employed for ascertaining the strength of soda and chloride of lime solutions, etc., is so graduated and weighted that the 0 or zero mark is equal to 1,000, or the specific gravity of distilled water at the temperature of 60° F., and each degree on the scale is equal to ·005; so that by multiplying this number by the number of degrees marked on the scale, and adding 1·, the real specific gravity is obtained. Thus 10° Twaddell indicates a specific gravity of 1050, or 1·05, and so on.

Imitation Manilla Pulp from Wood.—Mr. George E. Marshall, of Turner's Falls, Mass., patented a process some years back by which wood, under the action of hot water, and under a heavy pressure, acquires the characteristic colour of manilla. The wood, having been cut as usual, is placed in a closed vessel or tank capable of resisting high pressure, if necessary, of 450 lbs. to the square inch, the material being closely packed. At the bottom of this tank is an opening with a valve, through which the water, previously heated to a point above boiling, and below 280°, is forced by a hydraulic press to such an extent as to saturate and to completely permeate the wood, and to soften and drive out of the pores the gum, resins, and acids; and if the temperature is kept sufficiently hot, it gives the pulp the desired colour belonging to a finely-made manilla paper. This may be aided somewhat by the introduction of a small quantity of some alkaline substance to act on the acids. The water may be heated in a coil outside, and forced into the tank by a hydraulic press. The water thus heated and forced in leaves the wood or the pulp in the most desirable condition for work and for colour. Pulp made from wood treated below the boiling point will be white; but this process is said to secure the desired manilla colour by raising the temperature to 240° or 250° for a light pulp, and as high as 280° for a dark pulp. No pressure is required from the steam above three atmospheres, but the press may give from 450 to 500 lbs. to the square inch, and practice has shown that the greater the pressure the more speedy is the operation on the wood.[36]

Testing Ultramarines.—The sample of ultramarine should be examined as to its power of resisting the action of alum solutions, which may readily be done by the method suggested by Mr. Dunbar:—"Dissolve the same amount of each sample in water, and mix in this water about ½ lb. of pulp. When thoroughly mixed, and each lot of pulp is well and evenly coloured, add one glassful of the ordinary mill alum liquor, either from pure alum, or aluminous cake to each, losing no time over the operation. Stir each well and continuously with a glass rod, and note the glasses carefully as to the length of time each sample keeps its colour." To ascertain the staining power, so called, of the ultramarine, and at the same time the tone, or tint, which it will impart when mixed with pulp, 25 grains of each sample should be mixed with 100 of kaolin or sulphate of lime (pearl hardening) and the several mixtures then worked up into a paste with a little water by means of a spatula, when the differences in the staining power of the respective samples will at once become apparent if either be of inferior quality. To make the test more complete, a like amount of commercially pure ultramarine should be mixed with 100 grains of kaolin for the purpose of comparison. In this way a ready judgment may be formed as to the quality of the sample under examination.

Strength of Paper.—The comparative strength of samples of paper may he determined by cutting strips an inch in width from each sample, and suspending these from a rigid iron bar. Weights are then cautiously attached to each until the sample breaks, when the difference in the weights sustained by the respective samples before the breaking point is reached will determine the comparative strength of the samples tested. Mr. Parkinson, of St. George's Road, Preston, furnishes a simple contrivance for determining the breaking points of paper, and so comparing their value.