542 



KEPORT — 1880. 



The deviation, according to the average of the results of various ohservers, produced 

 by a plate of quartz, 1 mm. in thickness, is 2-4° for the mean j^ellow or transition 

 tint, and 21*66° for the sodium ray. Hence the above values for Sj may be calcu- 

 lated to the corresponding values for Sd, by mvdtiplying these by the factor 



21-66 



""24"" -9025. 



4. On the Identification of the Goal-tar Colours. By John Spiller, F.G.S. 



Dyers and others who are in the habit of using the coal-tar colours are familiar 

 with a number of chemical reactions by which the members of the series may 

 generally be classified and identified. Diflerences are remarked in their relative 

 affinities for various sorts of fibres, some colours being taken up freely by silk, 

 others fixing better upon wool, and some few, like saft'ranin, exhibiting a special 

 affinity for cotton. Again, as with the yellows, great differences are observed when 

 the operator proceeds to work with a free acid or a weak alkali in the dye bath, 

 primrose (naphthalene yellow), requiring the former, but not so phosphine (cry- 

 saniline yellow), which demands a neutral or even slightly alkaline bath. 



By the study of these conditions, aided by a few characteristic tests, it is often 

 possible to identify colouring matters of unknown or doubtful origin, and it is with 

 the \-iew of extending the number of such readily available tests that I recommend 

 a more frequent appeal to the colour-reactions with sulphuric acid. 



For this purpose but small quantities of material are required, a few grains 

 serving to impart a distinct colour to a comparatively large bidk of sulphuric acid, 

 and the resrdting indications are in many cases both specific and permanent. Oil 

 of vitriol, which so readily destroys nearly all organic structures, does not carbonise 

 any of the coal-tar colours, or does so only under severe conditions, as at high 

 degrees of heat. Even indigo and madder, although of true vegetable origin, are 

 known to yield up their colouring matters to sulphuric acid, the old processes of 

 dyeing depending upon this fact. In the manufacture of garancine from madder 

 the woody fibre and organised tissues are destroyed by the action of sulphuric acid, 

 whilst the alizarin glucoside sur\-ives, and with it Turkey-red goods may be dyed.^ 

 Instances might be midtiplied as proof that colouring matters, both natvu-al and 

 artificial, resist the attack of oil of vitriol, and the large class of sidphonates 

 (Nicholson blues, ' acid roseine,' &c.), may be cited as establishing the fact that 

 colouring matters are not so destroyed, but form combinations with sulphuric acid. 



If, then, the body imder examination be dissolved in strong oil of vitriol, a 

 colour-test is at hand, whereby useful inferences may be derived as to the nature 

 of the dye, and often its exact identity disclosed. A few direct confirmatory tests 

 may then be applied. 



The most remarkable colour-reactions are the following : — 



Magdala (naphthalene pmk) . 

 Safi'ranin .... 



Crysoidin .... 



Alizarin .... 

 Eosin 



Primrose (naphthalene yellow) 



CrysanUine .... 



Aurin ..... 

 Atlas orange .... 

 Atlas scarlet .... 



gives a 



blue black. 



„ grass-green, becoming indigo blue on 



strongly heating. 



„ deep orange, turning almost to scarlet on 



heating. 



„ ruby red or maroon. 



„ golden yellow. 



difiicidtly soluble, first yellow, and colour 

 discharged on heating, 

 gives a yellow or brown solution of marked fluo- 

 rescent character. 



„ yellowish-brown, non-fluorescent. 



„ rose colour, turning to scarlet on heating. 



,, scarlet solution, very permanent on heat- 



inar. 



See W. H. Parkin's 'History of Alizarin,' Jown. Society of Arts, May 1879. 



