PHYSICAL PROPERTIES OF PORTLAND CEMENT. 609 



in a pan and covered with a damp cloth, the cloth to be kept away 

 from them by means of a wire screen; or they may be stored in a moist 

 box or closet. 



43. Care should be taken to keep the needle clean, as the collection 

 of cement on the sides of the needle retards the penetration, while cement 

 on the point reduces the area and tends to increase the penetration. 



44. The determination of the time of setting is only approximate, 

 being materially affected by the temperatures of the mixing water, 

 the temperature and humidity of the air during the test, the percentage 

 of water used, and the amount of moulding the paste receives. 



STANDARD SAND. 



45. The Committee recognizes the grave objections to the standard 

 quartz now generally used, especially on account of its high percentage 

 of voids, the difficulty of compacting in the moulds, and its lack of 

 uniformity; it has spent much time in investigating the various natural 

 sands which appeared to be available and suitable for use. 



46. For the present, the Committee recommends the natural sand 

 from Ottawa, 111., screened to pass a sieve having 20 meshes per linear 

 inch and retained on a sieve having 30 meshes per linear inch; the 

 wires to have diameters of 0.0165 and 0.0112 inch, respectively, i.e., 

 half the width of the opening in each case. Sand having passed the 

 No. 20 sieve shall be considered standard when not more than 1 per cent 

 passes a No. 30 sieve after one minute continuous sifting of a 500 gr. 

 sample. 



47. The Sandusky Portland Cement Company, of Sandusky, Ohio, 

 has agreed to undertake the preparation of this sand, and to furnish 

 it at a price only sufficient to cover the actual cost of preparation. 



FORM OF BRIQUETTE. 



48. While the form of the briquette recommended by a former 

 Committee of the Society is not wholly satisfactory this Committee 

 is not prepared to suggest any change, other than rounding off of the 

 corners by curves of |-inch radius. 



MOULDS. 



49. The moulds should be made of brass, bronze, or some equally 

 non-corrodible material, having sufficient metal in the sides to pre- 

 vent spreading during moulding 



