462 



Popular Science Monthly 



the final disposal system may be made 

 intermittent by means of an automatic 

 siphon placed in the discharge chamber. 



-CI MANHOLE 



K-6^ 



TOP VIEIW 



Fig. 2 : A septic tank of larger dimensions suitable for a 

 family of eight persons, and one that can be used where 

 there is plenty of fall to carry away the liquefied matter 



Experience has determined that the 

 settling chamber of a small septic tank 

 should have a capacity of from 5 to 15 

 cu. ft., or from 40 to 80 gal. per person in 

 the family. The best results are obtained 

 when the capacity approaches a larger 

 limit, so that 18 to 36 hours' sewage from 

 the house may be held at one time, to 

 undergo sedimentation and bacterial ac- 

 tion for this length of time. Care should 

 be taken not to make the tank so large 

 that liquefied sewage remains in it more 

 than 36 hours, lest putrefaction set in. 



daily water consumption. Although a 

 depth of 3 ft. may be sufficient for some 

 classes of sewage, it is better to have the 

 depth from 4 to 8 ft., accord- 

 ing to the number of people, 

 in order to give the sludge a 

 good chance to settle and 

 liquefy. The width of the 

 chamber may ordinarily be 

 about one-third or one-half 

 the length, although this may 

 vary for economy and con- 

 venience. The width should 

 not be less than 3 ft., however. 

 The inlet from the house 

 should be provided with an 

 elbow, so that the discharge 

 will be at least a foot below 

 the contained sewage, thus 

 preventing disturbance of the 

 surface scum. The outlet 

 from the settling chamber 

 should be equipped in the 

 same way. Where the en- 

 trance and discharge velocities 

 are very strong, baffle walls of 



wood or concrete should be placed before 



these openings to break the current. These 



precautions are especially beneficial in the 



smaller sized 



tanks. 



The dis- 

 charge cham- 

 ber should be of 



such capacity 



and depth as to 



discharge 



about every 10 



or 12 hours. It 



may be desir- 



a b 1 e to d i s- 



charge at more 



or less frequent 



intervals 



according to the 



nature of the 



Fig. 4: An automatic 

 siphon that may be set to 

 operate at certain intervals 



Fig. 3: A double chamber septic tank for 

 use of six or more persons. It is practical 

 where the outlet fall is difficult to obtain 



For this reason one should make an accu- 

 rate estimate of the daily sewage flow, 

 which will be practically equal to the 



soil in the disposal area. 

 This action may be controlled by the arrange- 

 ment of the discharge chamlDer and the 

 siphon. Where little outlet fall is avail- 

 able it is possible so to construct the dis- 

 charge chamber that its floor will be consid- 

 erably above that of the settling chamber. 



The capacity and depth of discharge 

 chamber and the size of siphon will de- 

 pend on the number of persons served 

 and the means of disposal. If a sand 

 filter or a distribution system in 



