1826.] Cohuring Mailer of Lac. 403 



esteemed by dyers is formed of nitric acid specific gravity 1*170, 

 to which l-20th of muriatic acid specific gravity 1-190, has been 

 added. A notion formerly prevailed amongst practical men that 

 aquafortis should be kept in the carboys twelve months before 

 being used ; but if the nitrous gas be carefully separated, no 

 such length of time is required. 



To make the solution, 28 lbs. of aquafortis are poured into an 

 earthen vessel, the form of which is slightly conical ; this form, 

 by exposing a large surface, allows the gases formed during the 

 solution to escape. A single handful of finely granulated tin is 

 thrown in, and, when dissolved, fresh portions are added (stirring 

 carefully between each addition) until 4 lbs. have been dissolved; 

 the solution, after remaining 12 hours to cool and subside, is 

 ready for use. 



It is advisable to use the tartar (supertartrate of potash) ia 

 powder. 



For the shade of yellow required to form scarlet, young fustic 

 (rhus cotinus) in chips, inclosed in a bag, is used. 



The vessels employed for the dyeing of scarlet are of block 

 tin with copper bottoms ; some dyers use vessels composed 

 entirely of tin ; they are liable to accident from the melting of 

 the tin, if the fire be urged too violently, nor do they wear so 

 long as those of tin and copper. When the copper is kept well 

 cleaned, no deleterious action will occur. 



The first operation of dyeing is the mixing of the lac dye ; it 

 is performed in an earthen vessel of similar form to that described 

 for making the solution of tin. To each pound of lac dye, of 

 the quality of D. T. (ground to an impalpable powder) three- 

 fourths of a pint of lac spirit are added, and the whole mixed by 

 stirring with a wooden spatula ; this proportion will form a very 

 thick paste : four measured ounces of solution of tin for each 

 pound of lac dye are then poured in, and after being again well 

 mixed, the lac dye is left six hours to the action of the acid 

 before being used. 



Woollen cloths or yarns before being dyed are well cleaned 

 by fullers' earth and water, which, by removing any oily matter 

 that may adhere to them, and rendering the cloth equally wet, 

 facilitates the deposition of the colouring matter. 



For the dyeing of lUOlbs. of pelisse cloth (a broad woollen 

 cloth of thin and open texture), a tin vessel of the capacity of 

 300 gallons is nearly filled with clear water, and a fire lighted 

 in the furnace ; when at the temperature of 150° a dishful of bran 

 and half a pint of solution of tin are thrown in ; they, uniting 

 with any impurities floating in the water, form a scum upon the 

 surface, which is removed when the water approaches to 

 boiUng. 



When boiling, lO.V lbs, of D. T. lac dye previously mixed 

 with seven pints of lac spirit, and three and a half pints of solu- 



2 d2 



