460 0. D. von Engeln — Studies on Ice Structure. 



pushed forth. Two hours later the air temperature rose to the 

 freezing point and the pressure had fallen off to 2000 lbs. per 

 square inch. The air temperature continued to rise slowly, 

 and by 2 P. M. water from pressure melting began to ooze out 

 at the top of the cylinder between its bore and the steel plunger 

 but uo water came out of the lateral orifice with the ice rod, 

 which had meanwhile increased another two inches in length, 

 making 16 inches in all ; the load at the end being 1100 lbs. per 

 square inch. That the water oozing out at the top was from 

 pressure melting was indicated by the fact that it refroze in 

 feathery crystals on the outside of the cylinder. 



Microscopic sections cut on March 6th from the part of the 

 rod protruded at the lowest temperatures on examination proved 

 the ice to be perfectly clear, glassy and compact. Under crossed 

 riicols individual particles proved to be differently oriented 

 but exhibited parallel extinction within a given boundary. 

 The outer circumference was finer grained than at the core, 

 shear lines and breccia bands could be identified but there were 

 some apparently real crystal boundaries. "Undoubted breccia 

 bands and undoubted boundaries of breaking, but looks for all 

 the world like a medium-grained granite rock, with a very few 

 apparent crystal edges but not usually. The fact that this is 

 clear compact ice shows beautiful flow." (Tarr's laboratory 

 notes.) 



The downward bend of the rod may have been due to more 

 rapid emergence at the top than the bottom of the orifice. If 

 so, the differential movement may account at least in part for 

 the breaking and shearing. However, the rod may have bent 

 of its own weight or because of internal stresses. Clay squeezed 

 through like orifices in clay-working machinery bends down 

 similarly because of irregularities in the material. 



Interpretation and Application of the Experiments. — Ice 

 crystallizes in the hexagonal system. The habitus of the 

 crystals and their orientation vary according to their origin. 

 In the lake ice the ciwstals occur in bundles of prisms with 

 the basal planes of the mass parallel to the refrigerating 

 surface. In glacier ice more or less nodular grains, each a 

 crystal unit, form an interlocking aggregate with the principal 

 axes of the individuals variously oriented, although some 

 observers claim that there is a measurable tendeucy for the 

 grains in the basal layers of glaciers to be disposed with their 

 principal axes parallel to the direction of gravity. Water 

 freezing in crevasses in glaciers has been noted to develop 

 columnar ice crystals with principal axes extending at right 

 angles from the opposing walls of the fissure. In artificial ice 

 frozen in cans submerged in ammonia-cooled brine the crystals 

 have their principal axes extending radially from the outer 



