INTRODUCTION. 3 



CLASSIFICATION OF CEMENTING MATERIALS. 



GROUP I. SIMPLE CEMENTING MATERIALS: including all those cementing ma- 

 terials which are produced by the expulsion of a liquid or gas, through 

 the action of heat, from a natural raw material, and whose setting 

 properties are due to the simple reabsorption of the same liquid or 

 gas, and the reassumption of original composition; the set cement 

 being, therefore, similar in chemical composition to the raw material 

 from which it was derived. 



SUBGROUP I a. HYDRATE CEMENTING MATERIALS OR PLASTERS : manufac- 

 tured by driving off water from gypsum; setting properties due to the 

 reabsorption of water. 



SUBGROUP I b. CARBONATE CEMENTING MATERIALS OR LIMES AND MAGNESIA: 

 manufactured by driving off carbon dioxide from limestone or mag- 

 nesite; setting properties due to the reabsorption of carbon dioxide. 

 GROUP II. COMPLEX CEMENTING MATERIALS: including all those cementing 

 materials whose setting properties are due to the formation of entirely 

 new chemical compounds during manufacture or use; the set cement 

 being, therefore, different in chemical composition from the raw mate- 

 rial or mixture of raw materials from which it was derived. 

 SUBGROUP II a. SILICATE CEMENTING MATERIALS OR HYDRAULIC CEMENTS : 

 setting properties due entirely or largely to the formation of silicates 

 during the processes of manufacture or use. 



SUBGROUP II b. OXYCHLORIDE CEMENTING MATERIALS : setting properties 

 due to the formation of oxychlorides. 



The various groups and subgroups above noted will now be taken 

 up separately and briefly described, in order that the principles on 

 which the classification is based may be clearly understood. 



Group I. Simple Cementing Materials. 



The products included in the present group include those known 

 as "plasters", " hard-finish cements", "limes", and "magnesia." 



The material from which the "plasters" and "hard-finish cements" 

 are derived is gypsum, a hydrous calcium sulphate; while the limes 

 are derived from limestone, which is essentially calcium carbonate, though 

 usually accompanied by greater or less amounts of magnesium car- 

 bonate; and magnesia is derived from more or less pure magnesite, a 

 natural magnesium carbonate. 



On heating gypsum to a certain temperature, the raw material parts 

 readily with much of its water, leaving an almost anhydrous calcium 

 sulphate, known commercially as plaster of Paris. On exposing this 

 plaster to water, it rehydrates., and again takes the composition of 

 the gypsum from which it was derived. 



