RURAL ENGINEERING. 387 



fuel consumption when in the direct path of the prevailing winds. The founda- 

 tions should be of concrete for permanence, as a rule 8 in. in thickness, and 

 should be set in the ground at sufficient depth to give a good foundation and 

 to be below the frost line. Some soils require drainage around the walls to 

 prevent frost action. It is recommended on any house 30 ft. or over that the 

 eaves be placed at least 6 ft. above the level of the surface soil. Houses run- 

 ning east and west and north and south give equally good results. 



It is said to be more profitable on the whole to construct a greenhouse of 

 wide span owing to the great amount of room available, better control of 

 ventilation, reduced chance of disease, and lower cost of heating. The ad- 

 vantages ascribed to iron frame greenhouses are the small cost of upkeep, 

 solidity, small cost to heat, small glass breakage, lack of columns, and minimum 

 shade. The objection to this tjiie of construction is its initial cost. 



The greenhouse of pipe frame construction is considered an economical house 

 for the man requiring only a small house to be used with raised benches, but 

 with this form of construction in a house of any size so many supporting mem- 

 bers are necessary that the ground in the house can not be easily cultivated 

 with horses. 



The merits of separate houses over joined houses are pointed out as the ease 

 with which side ventilation may be secured, ease of temperature and heating 

 control, and the small liability of the spread of disease. Raised benches are 

 recommended for the small greenhouse grower and the solid beds for the com- 

 mercial grower. As regards heating, the gravity system of hot water heating 

 is recommended for small houses, while for larger houses some form of circu- 

 lator is necessary. For long houses or for large houses or large ranges the 

 use of steam for heating is considered advisable. 



Experiments on the oxidation of sewage without the aid of filters, E. 

 Ardern and W. T. Ix)ckett (Jour. Soc. Chem. Indm., 33 {191Jf), Xo. 10, pp. 

 523-536, figs. 2). — Investigations with regard to the aeration of sewage showetl 

 that the resultant solid matter obtained by prolonged aeration, which has been 

 termed activated sludge, has the property of enormously increasing the purifi- 

 cation effected by simple aeration of sewage and greatly intensifies the oxida- 

 tion process. The extent of the accelerating effect was found to depend upon 

 the intimate manner in which the activated sludge is brought into contact with, 

 and upon its proportion to, the sewage treated. To maintain the sludge at its 

 highest efficiency it was necessary that thex*e should not be at any time an 

 accumulation of unoxidized sewage solids. 



Temperature exerted a considerable influence on the oxidation process. The 

 purification effected was seriously diminished at temperatures constantly below 

 10° C. (50° F.). Up to 20 to 24° no material difference in the clarification 

 effect and general purification was observed, although nitrification proceeded 

 more rapidly as the temperature rose. At higher temperatures the clarification 

 effect was somewhat interfered with during the earlier peritxl of aeration, with 

 a consequent delay in the establishment of nitrification. Subsequently the rate 

 of nitrification somewhat increased. 



It is concluded " that under the conditions of experiment a well-oxidized 

 effluent can be obtained by the aeration of average strength . . . sewage in 

 contact with activated sludge for a period of fi'om 6 to 9 hours. The percentage 

 purification effected as measured by the usual tests is at least equal to that 

 obtained by the treatment of sewage on efficient bacterial filters. The i)eriod 

 of aeration naturally depends upon the strength of the sewage treated and the 

 degree of purification required." 



Sewage disposal in unsewered districts (Minneapolis, ilinn.: Bd. Health, 

 I191-i], pp. 15, figs. 8). — This pamphlet deals briefly with the water carriage 

 80967°— Xo. 4—15 7 



