Coal-tar Products. 221 



and, by a process commencing with the treatment of it with 

 chloride of methyl, dimethyl- aniline violet is obtained ; this is a 

 very much-used dye. 



I cannot say much about the further treatment and uses 

 of carbolic oils and creosote oils ; the value of the former as a 

 disinfectant is well known to you ; when it is treated with nitric 

 acid Trinitro-phenol or Picric Acid is produced, which gives a 

 delicate fast yellow dye. Its salts, such as the picrate of potas- 

 sium, are very explosive. 



From both creosote oil and carbolic oil Naphthalene is obtained ; 

 this is used in the production of the albo-carbon light. Until 

 late years it has had but little value ; now, however, many 

 beautiful colours are made from it. I may mention Magdala red 

 and Manchester yellow. 



By the oxidising action of nitric acid it is converted into 

 Phthalic Acid ; this is connected with the benzol series, as when 

 heated with excess of lime it is converted into benzene ; it is the 

 starting-point for the long series of colours known as the Azo- 

 compounds. 



I now come to a substance which I cannot dismiss quite so 

 lightly. If you refer to Table A, you will see that in the distill- 

 ation of tar a substance called Anthracene Oil is produced, 

 coming off above the temperature of 270°. By cooling and 

 pressing, the solid hydrocarbons are separated from the liquid 

 ones, which latter are either re-distilled or used as lubricants. 

 The solid portion is further washed and pressed into anthracene 

 cake. Its formula is C"ff °, and it boils at 360°. It was of little 

 use until the discovery by Grsebe and Lieberman that from it 

 could be produced Alizarine, the colouring principle of the madder 

 plant [Riibia tinctorum). Now this plant has been used for the 

 purpose of obtaining a red dye from time immemorial. The 

 process is said to have originated amongst the inhabitants 

 of Malabar and Coromandel, from whence it was introduced into 

 the Levant, where no doubt it received its name of " Turkey 

 Red." It gradually spread to Russia, France, and finally to 

 Great Britain. 



The plant itself yields only about 1 to IJ per cent, of coloar- 

 ing matter, and on this account many attempts were made to 

 isolate this latter, and in 1826 Colin and Robiquet obtained from 

 the plant a substance which they called alizarine. From time 

 to time further investigations were made, and in 1868 Grtebe 

 and Lieberman found, on submitting alizarine to a certain 

 process, that they obtained a substance identical with anthra- 

 cene ; they then reversed the process. A substance known as 

 " anthraginuone " (C"H*0") had previously been obtained from 

 anthracene by oxidation ; this was treated by Grjebe and 

 Lieberman first with bromine and then with caustic potash. As 



c2 



