28 LAC-DYE 



ing deep hue, and therefore of inferior value. The palest and finest shell -lac is brought 

 from the northern drear. It contains very little colouring matter. A stick-lac of an 

 intermediate kind comes from the Mysore country, which yields a brilliant lac-dyo 

 and a good shell-lac. 



Shell-lac, by Mr. Hatchett's analysis, consists of resin, 90'5 ; colouring matter, 0'5 ; 

 wax, 4'0; gluten, 2'8; loss, 1*8; in 100 parts. 



The resin may be obtained pure by treating shell-lac with cold alcohol, and filtering 

 the solution in order to separate a yellow grey pulverulent matter. When the alco- 

 hol is again distilled off, a brown, translucent, hard, and brittle resin, of specific gravity 

 1-139, remains. It melts into a viscid mass with heat, and diffuses an aromatic 

 odour. Anhydrous alcohol dissolves it in all proportions. According to John, it con- 

 sists of two resins, one of which dissolves readily in alcohol, ether, the volatile and 

 fat oils ; while the other is little soluble in cold alcohol, and is insoluble in ether and 

 the volatile oils. Unverdorben, however, has detected no less than four different 

 resins, and some other substances in shell-lac. Shell-lac dissolves with ease in dilute 

 muriatic and acetic acids, but not in concentrated sulphuric acid. The resin of shell- 

 lac has a great tendency to combine with salifiable bases ; as with caustic potash, which 

 it deprives of its alkaline taste. 



This solution, which is of a dark red colour, dries into a brilliant, transparent red- 

 dish brown mass ; which may be re-dissolved in both water and alcohol. Bypassing 

 chlorine in excess through the dark-coloured alkaline solution, the lac-resin is precipi- 

 tated in a colourless state. When this precipitate is washed and dried, it forms, with 

 alcohol, an excellent pale-yellow varnish, especially with the addition of a little tur- 

 pentine and mastic. 



With the aid of heat, shell-lac dissolves readily in a solution of borax. 



The substances which Unverdorben found in shell-lac are the following : 



1. A resin, soluble in alcohol and ether; 



2. A resin, soluble in alcohol, insoluble in ether ; 



3. A resinous body, little soluble in cold alcohol ; 



4. A crystallisable resin ; 



5. A resin, soluble in alcohol and ether, but insoluble in petroleum, and uncrys- 

 tallisable. 



6. The unsaponified fat of the coccus insect, as well as oleic and marganc acids. 



7. Wax. 



8. The laccine of Dr. John. 



9. An extractive colouring matter. 



Shell-lac is largely used in the manufacture of sealing-wax and varnishes, and for 

 japanning. 



ZjAC-DTE, Lac-LaJce, or Cake-lac, is the watery infusion of the ground stick-lac, 

 evaporated to dryness, and formed into cakes about two inches square and half an 

 inch thick. Dr. John found it to consist of colouring matter, 50 ; resin, 25 ; and 

 solid matter, composed of alumina, plaster, chalk, and sand, 22. 



Dr. Macleod, of Madras, states that he prepared a very superior lac-dye from 

 stick-lac, by digesting it in the cold in a slightly alkaline decoction of the dried leaves 

 of the Menecylon tinctorium (perhaps the M. capitellatum, from which the natives of 

 Malabar and Ceylon obtain a saffron-yellow dye). This solution being used along 

 with a mordant consisting of a saturated solution of tin in muriatic acid, was found 

 to dye woollen cloth of a very brilliant scarlet hue. 



The cakes of lac-dye imported from India, stamped with peculiar marks to designate 

 their different manufacturers (the best DT, the second JMcE, the third CE), are now 

 employed in England for dyeing scarlet cloth, and are found to yield an equally bril- 

 liant colour, and one less easily affected by perspiration than that produced by 

 cochineal. When the lac-dye was first introduced, sulphuric acid was the solvent 

 applied to the pulverised cakes, but as muriatic (hydrochloric) acid has been found 

 to answer, it has to a great extent supplanted it. A good solvent (No. 1) for this 

 dye-stuff may be prepared by dissolving 3 pounds of tin in 60 pounds of muriatic acid, 

 of specific gravity ri 9. The proper mordant for the cloth is made by mixing 27 

 pounds of muriatic acid of sp. gr. 1-17, with 1 J pound of nitric acid of 1'19 ; putting 

 this mixture into a salt-glazed stone bottle, and adding to it, in small bits at a time, 

 grain tin, till 4 pounds be dissolved. This solution (No. 2) may be used within 

 twelve hours after it is made, provided it has become cold and clear. For dyeing ; 

 three quarters of a pint of the solvent No. 1 is to be poured upon each pound of the 

 pulverised lac-dye, and allowed to digest upon it for six hours. The cloth before 

 being subjected to the dye-bath, must be scoured in the mill with fuller's earth. To 

 dye 100 pounds of pelisse cloth, a tin boiler of 300 gallons capacity should be filled 

 nearly brimful of water, and a fire kindled under it. Whenever the temperature 



