890 EXPERIMENT STATION EECORD. 



will give equal transverse strength, regardless of the thickness of the side 

 piece, provided it supplies sufficient bearing area. The transverse strength per 

 screw in yellow pine or oak varies directly as the square root of the pene- 

 tration into the middle piece, while in cypress it varies directly as the cube 

 root of the penetration in the middle piece. 



For a particular length of screw the smaller the gage the greater the strength 

 per pound of screws. As the length of screw is increased the strength per 

 pound is decreased, the gage remaining constant. As the number of screws 

 per pound is increased the strength per pound is increased, irrespective of 

 length or gage; the strength of a yellow pine joint is about 80 per cent, and 

 of a cypress joint about 40 per cent of that of an oak joint. There is no 

 apparent simple relation between gage or diameter and transverse strength. 

 The smaller the gage the more economical the screw, the length remaining con- 

 stant. The gage remaining constant, the shortest screws will be most eco- 

 nomical. 



Sun-power plant (Sci. Amer. Sup., 77 {WW, ^^o. 1985, p. 37, figs. 2).— A 

 comparative estimate of the cost of pow^er from coal and from solar radiation 

 " shows that the sun-power steam generator will compete in the tropics with 

 a coal-burning steam generating plant which can obtain its coal at a rate of 

 only $2.40 per ton delivered to the furnace doors. Any excess in the cost of 

 coal burning beyond this figure is clear profit in favor of the sun-power plant." 



Utilizing- waste heat of a small gas eng-ine (Power, 38 (1913), No. 27, pp. 

 922, 923, figs. 3). — This article describes and diagrammatically illustrates the 

 utilization of the heat carried off in the exhaust and jacket water from an 

 8-horsepower gas engine. The exhaust heat is utilized in a drying closet, and the 

 velocity of the exhausting gas as an exhauster for dust and dirt. The jacket- 

 water heat supplies hot water and hot chemical mixtures. 



An experimental study in multiple effect evaporation, N. Deeeb (Ha- 

 ivaiian Sugar Planters' Stu., Agr. and Chem. Bui. 42 (191Jt), pp. Jp\ figs. 9). — 

 This bulletin describes methods employed and reports results of three years of 

 experimental work in a number of mills with multiple effect evaporation under 

 continually reduced pressure. The exi:)erimeutal work included investigations 

 on such subjects as rate evaporation as influenced by the vacuum in the last 

 cell, by higher initial temperature, and by variation of the temperature of the 

 steam entering a cell of an evaporator and the temperature in the vapor space; 

 heat economy of evaporators ; and the evaporative capacity of quadruple-effect 

 vertical submerged tube and horizontal tube apparatus. General results and 

 conclusions are as follows: 



" The temperature difference in the first cell is a rough index of the rate of 

 evaporation. 



" The vapors in a multiple effect evaporator are superheated. 



" The calculated effect of self-evaporation in a multiple effect evaporator is 

 never realized, due to superheating of vapors and to short-circuiting of vapors 

 with the incondensible gases. 



" Not only is the rate of evaporation influenced by the gross temperature 

 difference, but it is also affected by the absolute temperature prevailing, in- 

 creasing as this increases. 



" Increase of the gross temperature difference by means of decreasing the 

 temperature at the cold end up to the temperature corresponding to a vacuum 

 of 27 in. gives a material and valuable increase in the rate of evaporation, 

 but this increase is not by any means as great as is obtained by a similar in- 

 crease in gross temperature difference obtained at the hot end by increasing 

 the temperature (or pressure) of the steam. 



