Dr. Bolley on the Theory/ of Dyeing. 497 



of dyed cotton cloth to an ash, and the determination of the base 

 of the mordant therein, serves as an indication of the nature of 

 the dyeing process through which the stuflPhas passed. 



After what has been said, we think we may veiy properly 

 excuse ourselves the trouble of further examining into researches 

 which contain so little that is conclusive. 



The researches of Chevreul, and the prior ones of Roard and 

 Thenard, which he appeals to in his treatise on the theory of 

 dyeing, are not numerous and varied enough to lead to a clear 

 characterization of the group of phsenomeua Avhich result from 

 the application of salt solutions to fibres. This circumstance, 

 and the conjecture that a reconsideration of the question would 

 in many cases lead to different results, were the inducement 

 to undertake a long series of experiments from which infor- 

 mation might be expected. Some of Chevreul's experiments 

 related to the withdrawal of sulphuric and muriatic acids from 

 their dilute solutions by fibrous substances. He determined 

 the strength of the diluted acid before the immersion of the 

 fibre, and after its digestion in the solution. This method is 

 the only exact one. 



Proceeding on this idea, and availing ourselves of the method, 

 now so perfect, of volumetric analysis, at the same time neglect- 

 ing none of the precautions usual in accurate gravimetric analysis 

 we may expect to obtain results free at least from the effect of 

 influences of unascertainable magnitude. 



The following fibres were made the subject of experiment : — 

 (1) yellow jNIilan silk, raw ; (2) the same, carefully scoured in 

 the laboratory ; (3) woollen yarn, washed and bleached j (4) clean 

 flock cotton. 



Preparatory to every experiment, a certain quantity of each of 

 these substances was suffered to remain in a thoroughly dry stream 

 of air from an aspirator at a temperature of 100° C. until it ceased 

 to lose weight. It was then allowed to become cool over chloride 

 of calcium in a closed flask (the same, in fact, in which it had 

 been dried), and was then weighed. The acids or salt solutions 

 in which the fibres were to be immersed were provided of the 

 proper degree of concentration, and in such quantities as to 

 suffice for repeated experiments with all four kinds of fibres. 

 These solutions were first accurately analysed by the volumetric 

 method, or otherwise. In each experiment, as nearly as possible, 

 ten times as much of the solution in cubic centims. was taken as 

 the weight of the fibre amounted to in grammes. After twenty- 

 four hours' immersion the fibre was removed and the liquid agaia 

 analysed. 



In this manner the effect of the natural moisture of the silk 

 and wool, which is often very considerable, was got rid of, and 



Vhil. May. S. 4. No. 123. Supi^l. Vol. 18. 2 K 



