282 EXPERIMENT STATION RECORD. [Vol. 43 



before the leaves appear and when the sap stream is able to carry the chlorin 

 to the buds and young leaves. 



TNT as a blasting explosive, C. E. Munrqe and S. P. Howell {U. S. D'ept. 

 Agr., Dcpt. Circ. 94 {1920), pp. 2.'f, flys. i2).— This report presents the results of 

 an, investigation conducted by the U. S. Bureau of Mines to discover the safest 

 and best methods of utilizing TNT for industrial blasting purposes. It de- 

 scribes the physical and chemical properties of different grades of the explosive ; 

 gives precautions to be observed in handling, packing, and preparation of 

 cartridges, and charging; presents the results of field tests in blasting stumps,, 

 rocks, and other work; and compares the results with those obtained from 

 dynamite. 



It was found that Grade III TNT can be successfully used for adobe shots 

 of bowlders, for removing stumps, and for splitting logs ; and will give results 

 equal to those given by 40 per cent straight nitroglycerin dynamite. It de- 

 tonates completely with a No. S electric detonator, detonates completely under 

 water, and detonates completely after a moderate immersion in wet holes. It 

 is concluded tliat the appearance of black smoke on detonation is not to be 

 taken as an evidence of incomplete detonation. 



Results obtained at the University of Wisconsin and the Bureau of Mines 

 explosives experiment station are also reported. Experiments on the water- 

 resisting properties of TNT showed that when both ends of cartridges of all 

 grades of TNT are redipped and not punctured they withstand water fully as 

 well as the dynamites. Grade III TNT in cartridges was found to resist 

 water from 1 to 72 hours or more, the time depending upon the density at which 

 packed and the nature of the cartridge. In all tests with Grade III TNT 

 the cartridges that were packed easily withstood the water better than those 

 that were packed hard. Grade III TNT had very much better water-resisting 

 properties than either of the other grades of TNT, especially when loosely 

 packed, and compared favorably with the dynamites tested. 



Of the three common grades of TNT the only one recommended for use in wet 

 holes in cartridge form is Grade III. Grades I and II may be used for wet work 

 if packed in completely redipped paraffined cartridges, provided they can be 

 charged without breaking the cartridges. No mention is made in these ex- 

 periments of the variable effect in detonation which may be expected from 

 submitting the TNT to different degi-ees of pressure. 



Experiments on the effect of soil moisture on the efficiency of dynamite, pre- 

 viously noted (E. S. E., 42, p. 384), are included. 



Cement in 1918, E. F. Bukchaed {U. S. Geol. Survey, Min. Resources U. 8., 

 1918, pt. 2, pp. IV+565-627, figs. 3). — Data on the production and use of cement 

 in the United States and foreign countries during 1918 are reportetl. There 

 was a marked decline in the output of cement in 1918, amounting to about 22 

 per cent as compared with the output of the previous year. 



The physical properties of magnesia cement and magnesia cement com- 

 pounds, R. J. RoARK {Bul. Univ. Wis., Engln. Ser., 8 {1917), No. 5, pp. 251- 

 331, figs. 39). — This bulletin presents the results of an experimental study of 

 the physical proiierties of magnesia cement and magnesia cement compounds 

 and of the factors affecting these properties. An important object of the in- 

 vestigation was the determination of physical tests which could be i-elied upon 

 to indicate the suitability or unsuitability of particular cements or compounds 

 for use as flooring material. 



A description of magnesia cement, its manufacture and uses, is given, to- 

 gether with a summary of the results of chemical investigations. 



