POPULAR SCIENCE 



COLLOIDS, OR THE MATERIAL OF LIFE 



By S. C. BRADFORD, D.Sc. 



{The Science Museum, London) 



The study of crystals may be said to be as old as chemistry. 

 In the Latin writings that purport to be the translations of 

 those of the Arabian alchemist Geber, the process of crystallisa- 

 tion is described, together with the principal chemical operations 

 such as distillation, filtration, and sublimation. In fact the 

 development of chemical science has depended, in no small 

 degree, on the possibility of this method of separating sub- 

 stances in the pure state. Doubtless the importance of the 

 crystal has contributed to the neglect, by chemists, of the 

 tarry and resinous materials that form a considerable part of 

 the yield of many of their processes. Except, however, for 

 the products of the laboratory, crystalline substances are rare. 

 Few of the objects seen around, whether natural or artificial, 

 are definitely crystalline. Their composition is amorphous or 

 colloidal. Crystals are found in mineral deposits and the 

 primitive rocks of the earth's crust ; a number are valued as 

 gems. But the materials of the surface, such as clay, flint, and 

 chalk, are mainly colloid. Except for sugar, our food is 

 colloid. Some items, such as jelly, starch, and milk, are typical 

 of this state. Indeed, the name " colloid " is derived from 

 colla, the Latin for glue or crude gelatin. 



The practical applications of colloid materials are so wide- 

 spread that volumes might be devoted to their description. 

 Processes essentially colloid in their nature have been employed 

 from early times. Instances may be found in brick-making, 

 tanning and dyeing, the manufacture of paper and soap, and the 

 extraction of sugar. Among the colloid articles of everyday 

 use may be mentioned, soils, slates, concrete, pottery, glass, 

 textiles, wood, rubber, pitch, resins, varnishes, paints, adhesives, 

 and photographic plates. Merely to enumerate them all would 

 be tedious. Evidently the science of colloids is of very wide 



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