278 The Philippine Journal of Science leie 



A study of Table III reveals that considerable change in 

 both the initial and final set is caused by the sodium sulphide. 

 The setting time is retarded by an addition of a small amount 

 of sulphide, but is accelerated after a certain amount has been 

 reached. For instance, with brand A the initial set is retarded 

 from five hours and fifteen minutes to nine hours and thirty- 

 one minutes, w^ith the addition of 6.11 grams sulphide per liter; 

 hov^rever, v^^ith the addition of 20 grams per liter, it is ac- 

 celerated to one hour and nineteen minutes. The final set goes 

 from nine hours and six minutes to twenty-two hours and thirty- 

 seven minutes and then to four hours and forty-eight minutes, 

 with the corresponding concentrations of sulphide. The table 

 shows that brands A and E are the most sensitive to the effect 

 of the sulphide; the former has the greatest range in setting 

 time, while the latter shows the quickest initial and final set 

 of all, that is, a sodium sulphide solution may either accelerate 

 or retard the set, depending on the concentration. In every case 

 the acceleration is greatest at some point between 0.02 and 0.21 

 gram per liter. As the quantity of sulphide becomes greater, 

 the retarding influence increases until equilibrium is established. 

 In most cases this point is between 0.43 and 5.93 grams sulphide 

 per liter. The accelerating effect is supreme from this time 

 on, and in general, the setting time is decreased with each increase 

 in sulphide. However, after the concentration of 5.93 grams per 

 liter is reached, further additions cause relatively small changes. 



EFFECT OF HYDROGEN SULPHIDE 



An experiment was carried on to determine whether or not 

 the effect of sodium sulphide shown in the above experiments 

 is due entirely to the sulphide radical or is partially attributable 

 to the sodium present. To decide this, a solution of hydrogen 

 sulphide was made by passing the gas into distilled water. 

 Alliquot portions were removed and analyzed. The solution 

 was found to contain 0.91 gram of sulphur per liter, present as 

 sulphide. Setting time and soundness tests were made on the 

 five brands of cement with this hydrogen sulphide solution. The 

 results are similar to those obtained with the sodium sulphide 

 solution having a sulphide concentration most nearly corres- 

 ponding to that of this solution. All the soundness tests were 

 satisfactory. The time of initial and final sets are given in 

 Table IV. 



