PART III. PROPERTIES OF CREOSOTES. 



CHAPTER I. COMPOSITION' AND CHEMICAL PROPERTIES OF COAL-TAR 



CREOSOTE. 



COMPOSITION OF COAL-TAR CREOSOTES. 



The heavy oils of coal tar that are usually known to the trade as 

 creosote oil and carbolineums are in general composed of compounds 

 of the aromatic series and are usually somewhat complex in their 

 chemical structure. The hydrocarbons, that is, those compounds 

 containing only carbon and hydrogen, are represented by members 

 of at least six subdivisions of the aromatic series. 



The simplest of these is the benzene series, in which fall such com- 

 pounds as benzene, toluene, and xylene. These are mainly low- 

 boiling compounds — boiling below 200° C. — and are lighter than 

 water, but, on account of the difficulty in separating these com- 

 pounds from members of other series having higher boiling points, 

 they may be found in the oils that are heavier than water.^ 



The next higher series is probably the indenes. These also are 

 low boiling, that is, they boil below 200° C, but in all probability 

 they are found in coal-tar creosote. 



The naphthalenes, of which naphthalene itself is the most impor- 

 tant member so far as creosote oil is concerned, have boiling points 

 between 200° and 270° C. when they are in the pure state. Some of 

 this series are liquid at room temperature, but naphthalene, the 

 parent of the series, is solid at ordinary temperatures, and, if it is 

 pure, melts at 80° C. and boils at 218° C. Naphthalene may be 

 present in almost any proportion in commercial oils. Samples of 

 creosote, examined by the author, have contained as high as 75 per 

 cent of oil boiling below 225° C, of which fully 75 per cent was 

 naphthalene. On the other hand, oils such as the carbolineums con- 

 tain practically no naphthalene. Acenaphthene might be termed a 

 derivative of naphthalene. It has a somewhat higher boiling point, 

 namely, 275° C. In the pure state this compound is a beautifully 

 crystallized white material, melting at 95° C. It is characterized by 

 its great solubility in hydrocarbon oils, especially those found in 

 creosote; hence it rarely, if ever, crystallizes out from the mother 

 liquor. Experiments at the Forest Products Laboratory seem to 

 indicate that the golden yellow oil, which occurs above the naphtha- 



1 Huntley, in a master's thesis offered at the University of Wisconstn, has shown that oils boUing as 

 low as 137° C. may be obtained from a supposedly high-boiUng (295° to 320° C.) fraction of coal-tar creosote. 

 These oils, although small in amount, were in all probability a mixture of xylenes and other of the higher 

 homologues. 



47 



