268 W. M. HAMLET. 



CaO + MgO 



M = 



Si0 2 +Al 2 3 

 the value of M in a good cement never being found to exceed 3. 



The formula, which it is proposed to call the Hydraulic Modulus, 

 is the ratio of the sum of the bases to that of the acid-forming 

 bodies and is now extended by including all the active bases and 

 acidic radicles thus : — 



CaO+MgO + K 2 + Na 2 



M = 



Si0 2 +Al 2 3 +Fe 2 3 

 and varies in value between 1*7 and 2-2. A good cement, satis- 

 fying all the physical tests gives a value lying within these limits. 



Acting upon this basis the Russian Government now specify in 

 their contracts that the hydraulic modulus shall not vary beyond 

 these figures either way ; it is also specified that the sum of the 

 amounts of magnesia and sulphur tri-oxide shall not exceed 3%. 



In order to ascertain for myself what results should be obtained 

 from a known and well tried Portland cement, I asked Mr. De Lisle 

 Roberts of the Public Works Department to give me a sample of 

 a cement that had satisfactorily passed his most rigorous time and 

 physical tests. That gentleman very kindly furnished me with a 

 sample of a cement that had given him the following results on 

 the neat cement : — 



Tensile strain after 3 days ... ... 607lbs. 



7 „ 7023hs. 



„ ,. 7 „ (hot bath test) 7585>s. 



Cement and Sand 1 : 3 

 Tensile strain after 7 days 235Bbs. 

 Ditto, 7 days in hot bath 2475>s. 



Provided with such a good cement I was anxious to see what 

 the hydraulic modulus would be, accordingly the following com- 

 plete analysis was made : — 



CaO 62-70 



SiO a 21-75 



