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



understood that the carefully grown crystals often lack these 

 rarer planes, but by the careful growing we obtain the correct 

 proportions as a whole. Some of these planes w T ould be 

 represented on a drawing as a very narrow plane, while on the 

 actual crystal this part might have a sharp edge with no trace 

 of a plane. Our carefully grown crystal can be filed off and 

 made round on the edges, and then grown again for a short 

 time to brighten the surfaces, and then the rare planes can be 

 looked for. 



Further, it should be noted that the distortion which results 

 from the crowding of growing crystals, for the reason that it 

 gives rise to an unequal distribution of growing material, will 

 often cause the broad development of planes which may be nar- 

 row or absent in the carefully grown, suspended individuals. 

 To give such planes unnecessary prominence on a drawing 

 that is designed to show a naturally proportioned crystal would 

 be incorrect. If the drawing was for the purpose of merely 

 showing the position and intersection of the planes, it would 

 be admissible. 



As a rule, a system of weeding out will have to be followed 

 to prevent useless growth from absorbing too much of our 

 growing material. That is, if we aim to produce large crystals. 



When a crystal is taken from a solution, it should* be blotted 

 off at once with absorbent paper in order to preserve its bril- 

 liancy. Before returning it to a fresh growing solution, it 

 should be dipped in water for a short time to insure that no 

 abnormal growth can take place from unobserved nucleii that 

 may be adherent. 



It is desired to awaken interest in the subject, and to give a 

 partial idea of what we may hope to accomplish by such 

 experiments, and also to suggest that the habits acquired by 

 working over incompletely developed crystals may at times 

 lead us to overlook some things that may be of importance. 

 In growing crystals with this object in view, the highest suc- 

 cess will be likely to follow a slow, constant and uninterrupted 

 deposition, together with the necessary careful control of tem- 

 perature. 



New Haven, Conn., February 15th, 1915. 



