68 KEPORTS ON THE STATE OF SCIENCE.—1918. 
19 Fischer & Hooker, Koll. Zeit. 18, 129 (1916). (Casein Solutions.) 
20 Shorter, Journ. Soc. Dyers § Cols., 81, 64 (1915); 32, 90 (1916); 34, 136 
(1918). 
21 Shorter & Ellingworth, Proc. Roy. Soc., A. 92, 232 (1916). 
22 Pickering, Trans. Chem. Soc., 111, 96, (1917). 
23 Shorter & Harrison, Journ. Soc. Dyers & Cols., 34, 163 (1918). 
24 McPherson & Heys, #.P., 5620 (1909) ; 20089 (1909) ; 8478 (1915). 
25 McBain & Taylor, Ber. 48, 321 (1910). 
26 McBain & Taylor, Zeit. phys. Chem., "76, 179 (1911). 
27 Bowden, Chem. Soc. Trans., 99, 191 (1911). 
28 McBain, Cornish & Bowden, ibid. 101, 2042 (1912). 
29 Bunbury & Martin, ibid. 105, 417 (1914). 
30 McBain & Martin, ibid. 105, 957 (1914). 
31 Lairg. ibid. 118, 435 (1918). 
32 McBain & Bolam, ibid. 118, 825 (1918). 
Dyeing. 
The large amount of work carried out on dyeing has already been 
fully considered by King in the first report. The electrical theory 
of dyeing has recently been discussed at some length.*? In its pre- 
sent condition? four factors are taken into account. 
1. Molecular movement, by which dye molecules or particles 
transport themselves on to the fibre or into its pores. In true solu- 
tion, this process is usually known as diffusion and must be taken 
into account in all theories of dyeing. In colloidal solutions the 
same thing occurs but to a less extent. 
2. The electrical charge on the fibre and on the dye. The poten- 
tial of this charge has been measured under several conditions as 
regards nature and concentration of added electrolytes. The nature 
of this contact potential has received much discussion; some 
chemists consider it to be due to residual valency. The opposite 
view that valency is the direct result of the electrical construction of 
elements is more likely to be true. In any case, Bragg’s models of 
crystals show that the surfaces of solids must behave differently from 
the bulk of the material. 
3. The size of the pores in the fibre. 
The presence of these pores has been directly proved by ultra- 
microscopic examination and indirectly by the fact that colloidal 
solutions can penetrate to a considerable extent into the fibres. The 
idea that dyes are imbibed into the cavities and pores of fibres by 
capillary attraction was put forward by Crum more than 50 years 
ago. The manner in which the dyes were fixed in those pores was, 
however, not explained by Crum, but has been explained as a case of 
electrical coagulation. 
The increased dyeing produced with cotton on mercerisation has 
been shown to be due to changes in the colloidal state of the fibre as 
well as electrical charge. The effect of drying on mercerised cotton 
is to reduce its dyeing capacity ; this has been explained as being 
due to reversion of the changes produced by mercerisation. 
4, The size of the dye particles. 
It is obvious that the extent to which dye particles can penetrate 
into porous substances must depend on their size. The rapidity of 
coagulation is also dependent on the size of the particles, 
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