410 EDITORIAL. 



Tlie above experiments show that piiso-puso and (melaza) increases the 

 initial rapidity of hardening, but the indications are that in the final 

 set the tensile strength is the same or somewhat less than when water is 

 used alone. 



In recent years tests of the influence of a great many indifferent 

 substances have been made on the hardening of mortar with small jjositive 

 or negative results. 



Parsons and Porter- experimenting with Portland cement found that 

 the addition of sugar or molasses delayed the setting of the mortar, the 

 retardation being greater when molasses was used, but when certain pro- 

 portions were not exceeded, the strength of the mixture was slightly greater 

 than that of the pure cement. Sugar apparently has no chemical action 

 on mortars. The variation of the binding power is due more to mechanical 

 causes and probably favors or retards the chemical reactions involved. 

 Eohland^ concludes that the hardening of cement is not due to the 

 formation of chemical compounds, but to a specific action of colloids, 

 and perhaps the same might be said of lime mortar. I believe that in 

 the final equilibrium few, if any, foreign bodies have a positive influence. 



The above-described use of puso-puso juice appears to give no explana- 

 tion of the extreme hardness of some of the old -mortars. In general 

 the hardening of lime mortar depends on the chemical reaction 



Ca(0H),-fC0,->CaC03+H,0. 



This reaction really exhibits two phases, namely, 



1. Ca(OH),^CaO+H,0 and 



2. CaO-FCO.-^CaCOj. 



The velocity of the reaction is extremely slow, requiring months, 

 years, and in some cases even hundreds of years to complete it. The 

 difficulty with which gases penetrate solid walls is shown by the fact 

 that reenforcing steel embedded in concrete will remain free from rust. 

 Keeently in tearing down a one-story building erected in 1902 at New 

 Brighton, Staten Island, all steel reenforcements were found in perfect 

 preservation excepting in few cases where they were allowed to come 

 closer than three-fourths inch to the surface.* Uncombined calcium 

 hydroxide has been found in mortar inclosed Ijetween very compact 

 stones after they had been in place three hundred years. In the light 

 of these facts the explanation of the superior quality of the old lime 

 mortars foiind in various places is probably that the porous stone so 



' Dinglcr's Pohjt. Joiirn. (1889), 271, 268; J. Soc. Chem. Incl. (1889), 8, 545. 



'Ztschr. f. Elektrochem. (1907), 13, 11. 



'Turner. H. C. Eny. Xeiis (1908), 59, 75: Anon. Jron Age (1908). 81, 348. 



