568 J. M. Blake — Grovring Crystals for Measurement. 



is important to work within limits which will not give rise to 

 noticeable currents during the deposit, since these currents 

 tend to cause irregular action on the parts of a growing crystal, 

 and may be expected to result in a loss of symmetry. We 

 wish to allow the natural forces that govern crystal growth, 

 unrestrained action, since the correct proportional development 

 of the planes should be one object of our measurement. 



The most familiar examples of artifical crystals are produced 

 by allowing saturated solutions to cool. Thus, very beautiful 

 large crystals are grown in the manufacture of salts on a large 

 scale, where the bulk of the solution is large, and the cooling 

 occupies considerable time. But these crystals, since they are 

 grown in groups, or attached to a support, have no chance to 

 complete their form. 



The writer had some success in working this cooling method 

 while using limited quantities of solution. This solution was 

 placed in bottles which were suspended in a large cask tilled 

 with hot water. The cask was packed in sawdust in a large 

 containing box. The crystals to be grown were suspended in 

 these bottles. This bulky apparatus might be replaced by a 

 smaller reservoir with a source of heat regulated by an adjust- 

 able thermostat. 



Two other plans will be mentioned which can be made to 

 give good results. The first is to fill a large test tube with 

 saturated solution, and support it in an inclined position. 

 This position is taken to prevent particles of salt from falling 

 upon the growing crystal. A small crystal is cemented to a 

 wire or splint, and supported centrally toward the bottom of 

 the tube. Next, a thimble made of fine brass wirecloth may 

 be pushed down the mouth of the tube an inch or more, and 

 the supply of material for growing is supported on this wire- 

 cloth, or, instead, the material may be retained in a cloth bag. 

 Heat is supplied to the upper part of the tube by a thin strip 

 of sheet copper one quarter of an inch wide, one end of which 

 is to be bent around the tube, and sprung on so that it can be 

 slipped up and down, and retain its position. 



The upper part of this strip, close to the tube, is twisted 

 one quarter turn, and also bent so that its surface takes a 

 horizontal position. A gas flame turned very low supplies 

 heat to the strip, and by adjusting the distance along the strip 

 the amount of heat supplied to the tube may be varied. This 

 distance may, at times, be five inches or more. This apparatus 

 can give a steady, constant growth to a crystal, and has given 

 good results. 



A second apparatus, which gave more freedom for suspend- 

 ing and removing the crystal, was made of a half-pint tumbler 

 having tapering sides. A copper wire was bent and tied into 



