36 MR. E. R. WATSON ON 



shades of these dyeings are proportional to the percentage of dye used. It was found 

 on examining the strips along with these standards, that it was fairly easy to say 

 what were the relative intensities of the exposed and unexposed portions of a strip. 



In the last column of Table I. the dye-stuffs are placed in Groups I — IV. according 

 to their fastness to light. In Group I. are placed the most fugitive, in Group IV. the most 

 permanent. 



This system of classification has been applied by Messrs. Cassella & Co., to a large 

 number of synthetic dyes (consult " Cotton Dyeing " published by the firm). The 

 groups to which the synthetic dyes employed belong are thus already known, and by 

 comparison with these we can at once determine into which groups the various indige- 

 nous dyes fall. 



The fo lowing peculiarities observed during the fading may be noted : — 



Latkan fades rapidly from orange to light pink, and then little further fading 

 occurs. This indicates that there are probably two different dye-stuffs in this material. 



Red Sandal and Padauk both darken rapidly on first exposure and become colder 

 in tint. Real fading sets in much later. 

 (II.) Fastness to washing with soap. 



The dyed samples were all treated with warm soap and water under the same 

 conditions. They were all steeped for 15 minutes at 6o'C. in an aqueous solution of 

 neutral soap containing 15 grms. per litre. [The soap was tested for neutrality previous 

 to use. It dissolved completely in absolute alcohol, and the alcoholic solution was 

 not alkaline to phenol phthalein]. The samples were afterwards washed, dried and 

 compared with the original dyeing. The dyes have been arranged in this way into four 

 groups, I. being the most affected by washing with soap and water , and IV. the least affect- 

 ed. These results are given in Table II, opposite. 



(///.) Fastness to Alkali. 



The dyed samples were all steeped for ten minutes in a solution of sodium carbo- 

 nate (10 grms. cryst. carbonate per litre) at 6o°C. washed, dried and compared with ori- 

 ginal. Also the colour of the alkaline bath after the steeping was noted (for 1 grm. 

 of cloth 250 cc. alkaline solution used). Roughly speaking, the faster the dye the 

 less the bath will be coloured. These results are given in Table III., and from them 

 the dyeings are arranged into four groups, I. being the most affected by the alkaline bath 

 and IV. the least affected. 



Together Tables II. and III. indicate the fastness of the dyeings to washing 

 under ordinary conditions. 

 (IV.) Fastness to Acid. 



The dyed samples were all steeped for one hour in 10 per cent, acetic acid solution 

 at 40 C. washed, dried and compared with the original. Also the colour of the acid 

 bath after the steeping was noted (for 1 grm. of cloth 250 cc. acid solution used). 

 Roughly speaking, the faster the dye the less the bath will be coloured. These results 

 are given in Table IV., and from them the dyeings are arranged into four groups, I. be- 

 ing the most affected by the acid and IV. the least affected. 



This treatment with acid measures the fastness of the dyeings to perspiration. 



