286 The Philippine Journal of Science isie 



air entered the flask, and immediately a solid rubber stopper was 

 placed in the neck. To the other capsule containing the cement 

 2.5 cubic centimeters of sulphide solution were added from a 

 burette, after which the whole was added to the second flask, 

 observing the same precaution as before. After shaking vigor- 

 ously to break up any lumps, the two flasks were placed in a 

 mechanical shaker and violently agitated for twenty-four hours. 

 Fifty cubic centimeter portions were withdrawn, while a stream 

 of hydrogen was passing, and the sulphate was determined. The 

 results indicated that a very small amount of the sulphide was 

 oxidized. 



According to Desch," ferrous sulphate may be formed in a 

 cement by the action of a sulphide, provided ferrous iron is 

 present. He says: 



Calcium sulphide, CaS, is often present to a very small extent in cements, 

 and is then derived from the reducing action of the fuel on calcium sulphate 

 contained in the raw materials or formed, in a stationary kiln, from sulphur 

 compounds in the fuel. Calcium sulphide is more characteristic, however, 

 of blast furnace slags. If the cement contains ferrous iron, this is con- 

 verted into the green ferrous sulphide which is generally considered to be 

 objectionable from its liability to undergo oxidation accompanied by expan- 

 sion of volume. 



While ferrous sulphate may be formed in some cements under 

 the above conditions, I believe it is not frequently formed in 

 quantities suflflcient to cause trouble — certainly not in any of the " 

 cements studied in the present investigation. The green color 

 produced by sodium sulphide solution is misleading because it 

 suggests the presence of ferrous sulphate, whereas various tests 

 have shown that no appreciable amount of this compound is 

 formed. 



REACTION BETWEEN IRON OXIDE AND SODIUM SULPHIDE 



With the object of obtaining further information on the 

 formation of the green color, ferric oxide was treated with 10 

 per cent sodium sulphide solution. After a few minutes the 

 mixture commenced to darken ; on warming on the hot plate the 

 red color disappeared entirely, and an examination showed that 

 the particles had become coated with a dark film. To study the 

 reaction further, weighed portions of ferric oxide were treated 

 with known volumes of the sulphide solution. Blanks containing 

 no iron were run for comparison. Each was made up to a definite 

 volume, and portions were removed for titration. The results 



" Loc. cit. 



