THE INDIGENOUS DYES OF BENGAL. 



161 



(/). Fastness to Light. 



Determinations carried out as in the case of cotton dyeings (Part I of this investi- 

 gation). The samples were exposed to light at the Civil Engineering College, 

 Sibpur, during January 1908 and the early part of February 1908, viz., on the follow- 

 ing days: January 2 — 11, 15 — 24, 26 — 31 ; February 1 — 6. The Sunshine Records of 

 the Alipore Meteorological Observatory were again utilised and the same correction 

 made for cloudy periods as in Part I. Again the day on which 8 - i hours of consecutive 

 sunshine were recorded was taken as the unit " one day of bright sunshine," in order 

 that the figures in this investigation should be directly comparable with the figures 

 recorded in Part I. It will be observed that the two investigations were carried out 

 in the same season of successive years. Moreover, by exposing along with the silk 

 dyeings a few samples of cotton dyeings prepared in the former part of the work, the 

 assumption that the figures in this paper and in Part I are directly comparable was 

 shown to be justified. 



In Table O the corrected values for the days of exposure are given : 



Table 0. 







Number of 



Value of day in 







Number of 



Value of 





Date. 



hours' sunshine 



arbitrary units. 



Date. 





hours' sunshine 



day in arbitrary 







recorded. 









recorded. 



units. 



January 2 



7-6 



0-98 



January 



21 



7-8 



0-99 





3 



7'9 



1*00 



» j 



22 



7-9 



i-oo 





4 



8-i 



i-oi 



5 ? 



23 



7-9 



i-oo 





5 



77 



0-99 



) > 



24 



7-8 



0-99 





, 6 



6-9 



0-94 



5 J 



26 



6-3 



0*90 





7 



8-i 



I'OI 



5 ) 



27 



6-o 



o-88 





8 



8-2 



I'OI 



,, 



28 



7'3 



0x6 





9 



7'5 



0-98 



J J 



29 



8-o 



I'OO 





1 I0 



7-i 



0-95 



J ) 



30 



8-i 



I'OI 





, 11 



7-5 



0-98 



J J 



31 



8-o 



I'OO 





15 



8-i 



I'OI 



February 



I 



8-2 



I'OI 





16 



8-2 



I'OI 



5> 



2 



7-0 



0-94 





17 



8-3 



1*02 



» ) 



3 



3*4 



072 





18 



8-i 



I'OI 



•> •> 



4 



7-6 



0-98 





19 



8-o 



I'OO 



3 ) 



5 



7-0 



0-94 





, 20 



7'5 



0-98 



t» 



6 



2-5 



0-67 



The results of the observations on the fading of the dyed samples are recorded 

 in Table I. In the last column of this table the dyeings 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. These groups are identical with the corresponding groups into 

 which cotton dyeings were classified, that is to say, a silk dyeing belonging to Group I 

 has the same fastness to light as a cotton dyeing which was classed in Group I ; and 

 so on. 



