16 BULLETIN 94<>, u. S. DEPARTMENT OF AGRICULTURE. 



Mix 50 grams of the material passing the 10-mesh sieve with — 3 grams of water 

 and knead with the hands into a spherical ball. Measure the diameter. Let this 

 ball drop from a height of — 3 cm. on a flat slab. Measure and record the reduction 

 in diameter and examine the surface for cracks. 



Usually the plastic character and adhesiveness of a good road soil can be judged by 

 the feeling of the mud made from the material, its adherence to the hands and its 

 stretch under light pulling. 



14. TESTS FOR QUALITY OF WATER TO BE USED IN CONCRETE. 



(1) Acidity and alkalinity. — The acidity and alkalinity test shall be made by immers- 

 ing strips of blue and red litmus paper in a vessel of the water for a period of five 

 minutes and noting color. A marked reversal in color indicates excessive acidity or 

 alkalinity and the necessity for further tests. 



(2) Total solids and inorganic matter. — Five hundred (500) cubic centimeters of the 

 water shall be evaporated to dryness in a weighed dish. For this purpose a platinum 

 dish of 100 to 200 c. c. capacity is found most convenient. The dish shall be nearly 

 filled with the water and placed on a water bath, additional portions of the sample of 

 water being added from time to time until 500 c. c. have been used. The contents of 

 the dish shall be evaporated to dryness and the dish and contents cooled in a dessicator 

 and weighed. The weight of the residue in grams divided by 5 is the per cent of total 

 solids in the water. 



(3) The total solids obtained as described, may consist of organic matter, of inor- 

 ganic matter, or of combinations of organic and inorganic matter. The platinum dish 

 shall be ignited at low red heat, and the darkening of the residue during the early 

 stage of the ignition usually indicates the presence of organic matter. The per cent 

 loss on ignition at low red heat will usually be an indication of the amount of organic 

 matter, but it should be noted that some mineral salts tend to volatilize or partly 

 decompose on heating. 



(4) The determination of the decomposition of the mineral matter in the water 

 usually requires a complete chemical analysis of the total solids obtained by the 

 evaporation of 500 c. c, or more, of the water, and is not generally undertaken except 

 when the percentage of total solids is large, or the water appears to give abnormal tests 

 in other respects. 



(5) A comparison of the given water with a water of known satisfactory quality can 

 be obtained by making standard soundness, time of setting, and 1 : 3 mortar strength 

 tests with standard sand, using the same cement c .standard quality with each water. 

 (Suggested limits for the last-named test are as folio s : Any indication of unsoundness, 

 marked change in time of setting, or a variation . . more than 10 per cent in strength 

 from results obtained with mixtures containing the water of satisfactory quality, shall 

 be sufficient cause for rejection of the water under test.) 



15. TEST FOR ORGANIC IMPURITIES IN CONCRETE AGGREGATES. 



The test recommended is described in the "Proceedings of the American Society 

 for Testing Materials, 'Philadelphia, Pa., Volume XIX, part 1, 1919, Appendix to 

 Report of Committee C-9 on Concrete and Concrete Aggregates." 



(1) The test as usually made consists of shaking the sand thoroughly in a dilute 

 solution of sodium hydroxide (NaOH) and observing the resultant color after the 

 mixture has been allowed to stand for a few hours. Fill a 12-oz. graduated prescrip- 

 tion l>ottl«' to the 4£-oz. mark with the sand to be tested. Add a 3 per cent solution of 

 sodium hydroxide until the volume of the sand and solution, after shaking, amounts to 

 7 ounces. Shake thoroughly and let stand for 24 hours. Observe the color of the clear 



1 No definite weight of water or height of fall recommended. 



