642 REPORT— 1888. 



air, and moisture. 2nd. Those on which lig-ht exerts a reducing action, which is 

 independent of the air, and in some cases takes place in the absence of moisture. 



Cadmium yellow, cadmium orange, king's yellow, crimson lake, and indigo are 

 placed in the first group ; these are bleached by light, under the conditions above 

 stated, but are permanent in an atmosphere of carbon dioxide, or in dry air. The 

 colours of the second group include Prussian blue, vermilion, chrome yellow, &c. 

 Prussian blue fades slowly in moist air — much more readily, however, in an atmo- 

 sphere of carbon dioxide ; but it is permanent in dry air. Mixed with cadmium 

 yellow, Prussian blue gives a green which is very sensitive to light if moisture is 

 present : permanent, however, in dry air. Vermilion is shown to fade in dry and 

 moist air ; also in an inert atmosphere like carbon dioxide. With cadmium yellow, 

 vermilion forms an orange which blackens in moist air in a few hours, though 

 iu dry air light is without action on it. The author condemns as unsafe those 

 pigments which fade in dry air, and shows that the greater number of paints are 

 stable in sunlight, provided moisture is absent. 



7. Further Researches on the Pyrocresols. By Dr. William Bott, F.G.8., 



and J. Bkuce Miller, F.I.C. 



In a paper submitted to the Chemical Section of the Association last year by 

 Professor Schwarz and W. Bott the properties and a number of derivatives of 

 the three isomeric pyrocresols, C]r,HjjO, were described. Since then experiments 

 have been made to ascertain the precise chemical nature of the reduction products 

 of o-pyrocresol. The products just referred to had been found to consist of a 

 mixture of paraffins, and a hydrocarbon, C,-,H^o, had been isolated from them. 



The reductions both with hydriodic acid and zinc dust have been repeated on 

 a larger scale and at a lower temperature, with a view of obtaining an intermediate 

 compound of an aromatic nature. No such product could, however, be obtained, 

 tlie reaction invariably giving rise to formation of paraffins only. The investiga- 

 tion of these paraffins is not yet completed, but we expect to be able to publish the 

 details before long, as well as the results of further study regarding the replacement 

 of the oxygen atom in pyrocresol by chlorine by means of phosphorus pentachloride. 

 The present paper only treats of a number of new derivatives of a-pyrocresol 

 which have been prepared during the course of the main investigation. 



Trichlor-a-pyrocresol, Cj,,H,,Cl.,0, is obtained by the protracted action of chlorine 

 upon a solution of a-pyrocresol in chloroform or carbon tetrachloride and repeatedly 

 recrystallising the product from boiling benzene. It forms a white bulky mass 

 consisting of very fine needles, which under the microscope are resolved into pretty 

 and characteristic aggregates of thin, transparent, flat prisms or bars. The sub- 

 stance is insoluble m water, alcohol, ether, acetic acid ; more soluble in chloroform 

 and carbon tetrachloride, and readily soluble in boiling benzene. The melting- 

 point is exceptionally high, but cannot be exactly determined, as the body melts 

 very gradually, first showing signs of fusion about 225°. 



Tetra-amido-a-pyrocresol oxide, Ci5Hs(NII.,),0.j, has been prepared by reduction 

 with tin under pressure of tetra-nitro-a-pyrocresol oxide suspended in a mixture of 

 "lacial acetic and hydrochloric acid. It is a greenish yellow powder, slightly 

 -soluble in water, sparingly soluble in alcohol and ether, and almost insoluble in 

 benzene. The salts are soluble in water, and with sodium hypochlorite give a 

 dark reddish-brown coloration. A double platinum chloride has also been pre- 

 pared. The melting-point appears to lie considerably above 300°. 



The amido-compound can be diazotised and the diazo salts obtained react with 

 phenols. Experiments in this direction were made with oxy-quinoline, resorcin, 

 thymol salicylic acid, cresol, phenol, a- and /3-naplithol. The derivative obtained 

 with i3-naphthol has been examined more closely and would represent the first 

 colouring matter obtained from pyrocresol. It is obtained by adding an alkaline 

 solution of ^-naphtbol to a diazotised acid solution of the amido-compound and 

 forms a dark red precipitate insoluble in water but soluble in ether, alcohol, 

 chloroform, and benzene. With strong sulphuric acid it gives a very characteristic 

 and beautiful reaction, dissolving in the concentrated acid with a deep, greenish 



