788 EXPERIMENT STATION RECORD. IVol. 37 



gravel without reference to its grading, will not necessarily produce the best 

 concrete. A poorly graded, coarse aggregate will unquestionably require more 

 mortar than will a well-graded one. Likewise, a coarse aggregate containing 

 a large amount of small stone will allow the use "^f a somewhat finer sand 

 than when the larger-.sized stones predominate. ... It might be considered 

 practical to use a graded rather than a naturally occurring concrete sand in 

 such important work as concrete road construction if, by so doing, the life of 

 the pavement can be prolonged." 



The effect of alkali on Portland cement, K. Steik {M'yoming Sta. Bui. IIS 

 {1917), pp. 71-122, figs. 19). — Experiments are reported in which it was found 

 that cement put into solutions of alkali salts set as well as in water. " In 

 solutions of sodium sulphate CaS04.2H20 is formed. In solutions of magnesium 

 sulphate CaSO*, 2H2O, and Mg(0H)2 are formed. In solutions of sodium 

 chlorid a silicate is formed. The high percentage of sodium in this silicate is 

 likely the reason for the increase of insoluble sodium In cement. 



" Sodium chlorid in solution or its presence in solution mth other alkali 

 salts has its effect chiefly through a solvent action. 



" Of the .solutions tested, the 5 per cent sodium sulphate solution had the 

 greatest disintegrating effects. Solutions containing chlorids, sulphates, and 

 carbonates had the least effect. Mortars disintegrate faster than neat cement. 

 The formation of compounds with molecular volumes larger than the molecular 

 voJTirae of calcium hydroxid is not the cau.se of disintegration of cement. The 

 ultnnale cause of the disintegration of cement by alkalies is due to the alkalies 

 forming compounds with the elements of cement, which subsequently are 

 removed from the cement by solution." 



Spontaneous combustion as a cause of fires, A. R. Lamb {loica .S7«. Circ. 

 S6 {1917), pp. 4). — This circular deals with the spontaneous combustion of coal, 

 drying oils, and especially hay, and briefly outlines means of preventing it. 



" The self-heating of hay generally reaches a dangerous point about a month 

 or six weeks after being mowed or stacked. Means of prevention must . . . 

 be employed before this time. The most effective means is proper curing of 

 the hay before storing it. . . . The hay should be carefully cured until the 

 stalks are so dry that no moisture can be squeezed out by twisting a bunch 

 in the hands. It must also be free from outside moisture, as dew or rain, when 

 put into the barn. 



" If the hay has unavoidably been put into the barn when somewhat moist 

 it should be watched for signs of heating. The first evidence is shown in the 

 morning, a day or two later, when the mow is covered with moisture condensed 

 from the water vapor driven off In the heating. If the heating continues, 

 craters or openings may be found near the center of the mow. If gases or 

 pungent odors are driven off, the heating is great enough to be <langerous, 

 and the hay should be removed at once." 



Report of tractor ratings committee, R. Olney et al. {N. G. E. A. Bnl., 2 

 (1917), No. 12. pp. 7-9). — The reconnnendations of the committee are "that the 

 standard rating specifications for all tractors include belt horsepower, drawbar 

 horsepower, drawbar pull in pounds, and engine and tractive speeds . . . but 

 that for ordinary use in designating the different sizes or capacities of tractors, 

 a standard rating be adopted such as is at present in general use. For examjile, 

 tractors should be rated as 12-25. 10-20, 12-20. etc.. in which the double 

 nvnnlier represents the drawbar and the belt horsepower, respectively. 



"That the standard rating be on the following basis: (1) The drawbar 

 horsepower rating must express the horsepower tliat the manufacturer will 

 guarantee his tractor — when in good condition and properly operated at normal 

 engine speed — to deliver at the drawbar continuously for two hours on a firm. 



