J. M. Blake — Growing Crystals for Measurement. 569 



a hoop which could be crowded down one inch from the 

 top of the tumbler. Cotton cloth was stitched upon this hoop, 

 and a one-half inch hole hemmed in its center. This formed 

 a shelf to support the feeding material, while the crystal to be 

 grown was hung by a thread to a wire placed across the hole. 

 The heat was supplied by a resistance element consisting of 

 two feet of No. 35 resistance wire doubled on itself, and wound 

 spirally around a copper wire. The two ends were soldered to 

 thicker wires for connecting. These wires were then var- 

 nished and inclosed in a small rubber tube with only the 

 thicker connecting wires projecting from one end. Both ends 

 of the rubber tube were cemented, to exclude water, and the 

 tube was then bent into a circular shape to be stitched to the 

 lower side of the cloth shelf, but, first, the connecting wires 

 together with one end of the rubber tube were brought up 

 through the cloth shelf, a hole being made for this purpose. 

 The top of the rubber tube was made to stand a trifle below the 

 top of the tumbler, while the wires passed out over its edge. 

 The mouth of the tumbler was covered with a glass plate. 

 Heat was obtained from a small six volt door-bell transformer 

 connected to the street current. 



Another successful plan was tried later. This was to wind 

 the resistance wire around the outside of the test tube, or the 

 neck of a long, wide-mouth vial, and coat the wire with varnish 

 to prevent short circuit. The material for growing was sus- 

 pended in a small cloth bag, and the vial was tilted so that the 

 growing crystal would swing free from the sides. 



This apparatus was used for growing crystals for measure- 

 ment, and for experiments on supercrystallization of isomor- 

 phous salts. Also, some experiments were made to produce 

 planes that are not of frequent occurrence, but which actually 

 belonged to the species under treatment. For instance, a 

 sphere of the salt was ground and polished, and was then 

 grown a short time. This gave every plane a chance to 

 assert itself, and the peculiar change the polished sphere took 

 on after a very short growing treatment was very interesting. 

 The light could be flashed from the line step-like surface 

 growth, and when mounted for measuring, the zone system of 

 measurement which the writer advocated many years ago, 

 could not very well fail to bring out the full complement of 

 planes. See this Journal, May, 1866. 



This experiment led to a possible explanation for the occa- 

 sional finding of rare and exceptional planes which might be 

 formed when crystals have been rapidly and partially dissolved, 

 but certain rounded surfaces were still left ; and this solution 

 was followed by a cooling, and a deposit of the salt which 

 might result in developing the rare planes. It should be 



