xm, A, 1 Witt: Cement and Concrete 47 



of the resulting calcium compounds nor the negative ion. 

 It is chiefly the positive ion. Both zinc salts and both 

 copper salts show similar effects, whereas the other chlo- 

 rides and sulphates behave differently. Since calcium sulphate 

 is difficultly soluble and calcium chloride is readily so, no division 

 can be made on that basis. There are one or two exceptions to 

 this effect of the zinc and copper compounds which are difficult 

 to explain. These are the effect of copper chloride on sample 

 III and the effect of zinc sulphate on sample I. However, in 

 most cases all the cements are affected similarly by the same 

 substances. 



A number of statements appear in the literature which attempt 

 to account for the effect of electrolytes on cements, but usually 

 there can be found as many exceptions as there are instances 

 of agreement. For instance, Dobrzynski " found that the nor- 

 mal consistency of cement, when gauged with solutions of various 

 chlorides, varied with the solubility of the salt. In the present 

 work, cements gauged with sodium, copper, and zinc chlorides, 

 which differ widely in solubility, showed the same normal con- 

 sistency (Table IV) . Kallauner is of the opinion that all soluble 

 calcium salts decompose cement. This is not in conformity with 

 other work with calcium salts (Table I). Though many believe 

 that the major effect of an electrolyte is due to the effect of the 

 negative ion, especially in so far as this may be able to affect 

 the solubility of the calcium compounds in the cement, the pres- 

 ent results do not indicate this. The statement of Rohland in 

 various papers that cement is affected by catalizers positive and 

 negative is not an adequate explanation. There are instances 

 in which the great change in the setting time of cement caused 

 by electrolytes seems to be catalytic, but in most cases the rela- 

 tion betweep the effect and the amount of the electrolyte present 

 suggests some physical or chemical influence which is not 

 catalysis but which has not as yet been explained. 



SUMMARY 



Investigation of the effect of certain substances on cement 

 is becoming more important because of new industrial uses 

 for concrete. The practical importance and the theoretical in- 

 terest of the subject have led to the publication of a number 

 of papers. 



A study of these papers reveals that, while a number of them 

 have individual merit, the results are not comparable and the 



" References are given in Table I. 



