JOURNAL OF THE SOCIETY OF COSMETIC CHEI•ISTS worthy of note that many pigments are now produced in presence of, or subsequently treated with, surface active agents which are undoubtedly adsorbed upon the surface of the pigment particles. There are so many of these surface-active agents available commercially that it would not be possible, within the scope of this paper, to give any real informa- tion about them except to say that the majority probably belong to one of the three following types: (a) sulphonated alcohol, petroleum extract or castor oil (b) alkyd naphthalene sulphonic acids (c) quaternary ammonium com- pounds Their very general use in industry proves that they are perfectly safe to handle--whether there is a minor- ity upon whom they act as irritants we cannot say. T• EOSINES The eosines are also worthy of special mention since they are unique in being precipitated as lead salts usually in the presence of some lead sulphate. The undertone of these lakes is often modified by adsorption upon them of a small quantity of one of the Rhodamines. The colour of the lake depends very largely upon the quality of the dye from which it is produced. Several samples of (allegedly) the same dye will give quite different products, particularly so far as brightness of the finished lake is concerned. They are, of course, much yellowet in colour than the madder lakes, and in your indus- try must suffer severe restrictions in use because of the presence of lead-- their relatively poor light fastness also curtails their use. The author spent some time about fifteen years ago endeavouring to prepare eosine lakes of improved light fastness and reduced toxicity. Some progress in the first aim was achieved by the use of thallium as salt-forming metal this, however, did not reduce toxicity, and because of the high price of the metal the work was not continued. Very many other lakes are known and produced commercially both from acid dyes by the process dis- cussed, or from basic dyes by an analogous process using a different substratum, e.g., calcium phosphate. Most of them possess the disadvan- tage of very poor light fastness, although it would be wrong to assume, and a grave fault on our part if we have conveyed the impres- sion, that of the various commercially available lakes only madder lakes possess good light fastness. With the exception of Pigment Green B, which is the iron salt of •-nitroso-•mapthol and pigment green 3B its simple modification, the toners of the metal-salt type, i.e., that typified by Permanent Red 2B, belong to the scarlet-crimson- maroon colour range. Here, again, such properties as fastness to light, resistance to attack of acids and alkalies vary so widely that no general comment can be made. One point is of interest and that is that 146

PIGMENTS as a whole this class of pigment is relatively non-bleeding in oils and waxes and is generally more resistant to attack by organic solvents than other organic pigments. The salt-forming metals in the case of these red toners is generally calcium or barium (much less fre- quently manganese or strontium). There appears to be very little published information on the toxicity of barium salts of these dyestuffs, although from personal contact with manufacturers of cosmetics we know that they are frowned upon. We were rather surprised, however, the first time we were informed, that even barium sulphate is viewed askance for no other reason than that barium and its salts are listed as poisonous materials. As outsiders to the indus- try we should have thought that the feeding of barium meal to patients immediately before abdominal X- ray photographs are taken would have been sufficient proof that this material is innocuous. Before leaving this section there is one point of terminology which might with advantage be clarified this concerns the use of the name permanent. A great many pigments appear in literature under this name, as, for example, Permanent Red 2B, or Permanent Red R, or Permanent Orange G. It should be clearly understood that, in this connection, the word "permanent" is merely a trade name and does not indicate a property of the pigment. The second type of toner, i.e., the dye acid complex, covers pretty well the whole spectrum except the yellow-orange range. They are of greater interest to the printing-ink maker and so far as the present authors are aware are not used in your particular industry at all. However, it is, perhaps, of interest very briefly to mention that the property which lends them greatest importance is their very high-staining power and, so far as the red pigments are concerned, their pleasing variety of tint on reduction, although when highly reduced they are not particu- larly fast to light. They are fairly good in their resistance to acid and alkali and generally possess negligible or no bleed in oils and waxes. They are, however, rather inclined to bleed in oxygen--containing organic sol- vents, a defect which limits their use in many fields. PIGMENT DYESTUFFS Coming now to pigment dyestuffs we enter a field which is expanding almost daily and, if we include the phthalo-cyanines in this class, one which covers the whole spectrum except the violet. The three chief factors which have led to the great diversity of this class of pigments are: (1) That certain compounds con- raining active hydrogen atoms can be substituted for naphthols--this discovery increased the colour range available. (2) That in certain cases diamines such as benzidine or substituted benzidines can be tetrazetised and coupled to give pigment dyestuffs with certain markedly improved properties. 147