112 



the remaining oil (livering). Under suspensoid pigments the adhesive 

 properties and cementing values of paint pigments apparently increase 

 with approach to coUoidal form. All paint pigments have colloidal 

 properties. Gardner found in the clear oil upon the surface of 

 specially prepared pigments which had stood for a year, the presence 

 of pigment material showdng Brownian movement on thinning with 

 benzols. Experiments made ^vith zinc oxide and with siUca ground 

 in linseed oil (thickened) gave even after thinning Mith four vols of 

 benzole a cloudy fluid which yielded no clarification on centrifuging, 

 but could be partially clarified by mixing the two fluids, a change 

 probably due to electric neutralisation. 



Paranitraniline red. in oil is clear and slightly coloured, becoming 

 bright red when benzole is added, a colour change common in the 

 case of many suspensoid sols. 



Prussian blue shows strongly Brownian movement and many 

 particles of chrome green suspensoids are coloured crimson, orange, 

 green, and blue in the ultramicroscope. 



Carbon black (contaming 90 per cent, carbon) probably adsorbs 

 linseed oil as in the case of pigments. In the presence of strongly 

 oxidised or boiled oils precipitation may occur on addition of benzene, 

 which may be due to imbibition of the spirit comparable Avith the 

 swelling of rubber in benzene or of gelatme with ■\\'ater. Again, if 

 zinc oxide or lithopone be ground in alcohol and linseed oil added, 

 the alcohol is displaced probably due to lo^^'ermg of surface tension 

 by introduction of the^oil. 



[An excellent summary of the properties and uses of carbon black 

 is given by Perrott and Thiessen (J. Ind. Eng. Chem. 12, 324, 1920,).] 



Ayres (J. S.C.I. , 35, 676, 1916) considers that "foots" from raw 

 linseed oil can be removed easily by heating to 100° C. and 

 centrifuging. 



The prebcnce of the mucilaginous material containing salts is 

 considered by some to be highly detrimental not only in the manu- 

 facture but in the durability of many mixings and paint coatings. 



Ware and Christman (loc. cit.) conclude that the use of emulsifying 

 agents in paint grinding to prevent hard setting has not been satis- 

 factorily explained. The emulsifying agent must exert no saponifying 

 action on the oil, but the presence of metaUie soaps in certain quantity 

 retards the settling. 



Hurst and Heaton state that the emulsification of the oil requires 

 to be assisted by metallic salts such as zmc sulphate, manganese 

 sulphate, and borax, &c. ; moreover the addition of a minute 

 proj)ortion of tannic acid incorporated with the pigment prior to 

 grinding with the oil causes the deflocculation of the pigment (Acheson, 

 J.S.C.I., 30, 1426, 1911). 



Cellulose varnishes have already been dealt with in previous 

 reports under nitrocellulose, celluloid, and cellulose acetate. 



A class of varnishes containing synthetic rosins on a phenolic 

 trioxy methylene basis is of growing importance. 



[Annual Reports of the Society of Chemical Industry (Paints, 

 Pigments, Varnishes, and Eesins, 1916, 17. and 18) and G. Matsumato, 

 Jour. Chem.^nd., Tokyo, 18, 434, 1915; J.S.C.I., 1104, 1915.] 



