692 EXPERIMENT STATION RECORD. [Vol.38 



feres with the cohesion. (2) When the colloid is precipitated a portion of the 

 dissolved calcium hydroxid Ls removed from solution. Since the latter sub- 

 stance is a very important factor in the strength of cement, it is to be antici- 

 pated that the strength will be lowered when some of it is removed. 



" It is probable that a number of other factors influence the effect of sulphid 

 on cement. Among these may be mentioned the fineness of the cement, the 

 temperature at which it is mixed, the percentage of water used, and the amount 

 of dissolved calcium hydroxid." 



Asphalt, related bitumens, and bituminous rock in 1916, J. D. Northkop 

 {U. S. Oeol. Survey, Min. Resources U. S., 1916, pt. 2, pp. II +263-281). —This 

 report discusses- the occurrence, distribution, and production of asphalt and 

 related bitumens, and states that " the quantity of natural asphalt, including 

 bituminous rock, grahamite, gilsonite, wurtzilite, and the native parafBn, 

 ozokerite, produced and sold at mines and quarries in the United States in 1916 

 was 98,477 short tons. This quantity was greater by 22,726 tons, or 30 per 

 cent, than the output in 1915." Data on imports and exports are also included. 



Investigations of gravel for road surfacing. T. R. Ago (Iowa Enyin. Expt. 

 Sta. Bui. 45 {1916), pp. 32, figs. 23). — Investigations are reported, the purpose 

 of which was to determine in a general way the character of the road building 

 gravels in the State of Iowa, to establish construction and maintenance methods 

 adapted to Iowa conditions, and to determine the possibilities of the use of 

 bituminous materials for the construction and maintenance of gravel roads. 

 Analyses of 151 Iowa gravels show that they do not contain as great a per- 

 centage of pebbles as is desirable in road surfacing material and not sufficient 

 clay to serve as a permanent binder, " yet the gravels do bind in time, show- 

 ing that some other element in the gravel is a factor in the bonding action." 



Experiments on methods of construction are also described, in which several 

 sections of road with gravel surfaces were constructed by the two-course trench 

 method, the single-course trench method, and as a single-course surface placed 

 on top of the earth road. A road was also constructed of river gravel. 



Experiments on the use of bituminous coatings on concrete surfaces are also 

 described. In one case it has been found possible to maintain concrete roads 

 in good condition by this method at a cost of not to exceed 2 cts. per square 

 yard per year. Further experiments showed " that only a very few materials 

 can be used for carpet coats on concrete and that they must be applied with 

 ext<reme care or they will peel off the surface." 



Experiments along this line in other States are reviewed and the conclusion 

 drawn that " the service value of a well-built gravel road is so much greater 

 than of the poorly built I'oads that it far outweighs the relatively small differ- 

 ence in cost. It is especially clear that it does not pay to skimp the materials 

 and it is an extravagance to construct a good road and then fail to keep it In 

 good repair. Gravel roads deteriorate very rapidly if neglected." 



Labor-saving machinery, C. I. Gunness {Mass. Agr. Col. Ext. Serv. Circ. 

 42 {1911), pp. 4, fiO^- 6). — The purpose of this circular is to call attention to 

 the machines which can be used to advantage in the raising of potatoes, corn, 

 beans, and other garden crops, and when possible to indicate the size of plats 

 which can be most profitably used. 



Buying a farm tractor, W. H. Sanders {Bien. Rpt. Kans. Bd. Agr., 20 

 (1915-16), pp. 123-145, figs. iS).— This is a review of the main factors influ- 

 encing the selection and purchase of a tractor for a Kansas farm, including 

 relative economy, first cost, depreciation, repairs, tractor types and speed, motor 

 styles, fuel, lubrication, and size and power ratings. The use of the tractor 

 on special kinds of work is also briefly discussed. 



