270 W. M. HAMLET. 



bodies, the phenomenon being known as the setting of the cement. 

 The stable bodies are silicates, alumina and iron compounds which 

 solidify together and resemble Portland stone, and hence the 

 name given to the product known as Portland cement. 



The particular kind of silicate formed is first the silicate of 

 lime — calcium orthosilicate (Ca 2 Si0 4 ) — formed by the combina- 

 tion of two molecules of lime with one molecule of silica. 



This view accords with the analytical results obtained with 

 Mr. Roberts' cement and is not taken for granted as some writers 

 seem to have done, where one, two, three, and even four molecules 

 of lime have been assumed to be the combining equivalent. 



From a careful examination of the pats of neat cement the 

 silicate appears to resemble, from the mineralogical point of view, 

 a, lime peridote, Ca 2 Si0 4 . The alumina acts as a body having 

 feeble acid properties forming an aluminate of the composition 

 3 CaO, A1 2 3 , while the ferric oxide combines with one molecule 

 of lime to form calcium ferrite CaO, Fe 2 3 . After proper setting 

 these compounds, including the hydrate, form a dense stone-like 

 substance of which the briquette, made with the cement in question 

 and now exhibited, is an example. 



On examination of a thin section of this briquette, made like any 

 other rock slice, all these compounds are visible, including the 

 magnesium silicate which is plainly seen when viewed with 

 polarised light, the iron-lime compound or ferrite is quite plainly 

 visible as well as the tabular crystal of calcium hydrate. The 

 crystals of the calcium silicate have no action under the crossed 

 nicols and appear most numerous in the crystalline cut section. 



It is evident therefore that in Portland cement we have the 



basic bodies : — 



CaO, MgO, K 2 0, Na 2 0, 



and the acidic radicles : — 



Si0 2 , A1 2 3 , Fe 3 3 , S0 3 , C0 2 , 



the percentages of which give us the elements for obtaining the 



hydraulic modulus of Le Chatelier. 



