6 CITY STREET SWEEPINGS AS A FERTILIZER. 



and pot 5 with stable manure. The illustration shows again that the 

 sweepings are beneficial, the plants in pots 2, 3, and 4 being larger 

 than in the untreated pot 1. Pot 4, which contains the soil treated 

 with decomposed sweepings, has smaller plants than any other except 

 the check. It will be recalled that this treatment showed the least 

 effect also in the case of wheat and corn. Pot 5, which is treated with 

 stable manure, has produced the largest growth, which again shows 

 that the sweepings are not as helpful as good stable manure. 



EXAMINATION FOR MINERAL OIL. 



The sweepings, as was pointed out, are apt to contain lubricating 

 oils and fine particles from the decay of the paving materials, which 

 may be a factor in determining their usefulness as a fertilizer material. 

 In order to study this point the three samples were repeatedly 



FIG. 1. Effect of street sweepings and stable manure on corn. (1) Soil untreated; (2) soil + stable ma- 

 nure; (3) soil + sweepings No. 1; (4) soil + sweepings No. 3;. (5) soil + sweepings No. 2. 



extracted in an extraction apparatus with petroleum ether until the 

 solvent was no longer colored. The fatty material was saponified with 

 alcoholic potash and the amount of mineral oil extracted by petro- 

 leum ether determined. Sample No. 1 contained 1.7 per cent, 

 sample No. 2 contained 2 per cent, and sample No. 3 contained 2 per 

 cent of the crude mineral oil. This high content of mineral oil sug- 

 gests the possibility of the recovery of low-grade lubricating oil from 

 city street sweepings, especially in those cities which have consider- 

 able automobile traffic. 



EFFECT OF THE OIL ON GROWTH. 



The effect of the oil extracted from the sweepings on growth was 

 tested with wheat plants. The young wheat seedlings were grown in 

 distilled water and nutrient solution cultures. Fifty milligrams of oil 

 from each sample was put in the culture bottles containing 250 c. c. of 

 solution. The oils from all of the samples were harmful to growth, 



