90 hostkttkr: apparatus for growing crystai<s 



(H) before striking any crystals. The stirrers are of silver. 

 A coil of small lead pipe (W) serves as a water jacket for one of 

 the tubes connecting the thermostats. The openings (O and d) 

 permit the removal of volunteer crystals, in case of accident, 

 without disconnecting the entire apparatus; for a similar reason 

 the return tube is cut at (R) and the platinum gauze filter fF) 

 may be detached. The entire apparatus is packed with felt in 

 a large, wooden box. 



The degree of supersaturation of the solution entering the 

 crystallizer may be controlled by adjusting (i) the temperature 

 difference between the saturator and the crystallizer, (2) the 

 rate of circulation between the two thermostats, and (3) the 

 temperature and the rate of flow of the cooling water in the coils 

 at (W). The difference in temperature between the saturator 

 and the crystallizer that is permissible depends upon the change 

 of solubility with temperature, and especially upon the extent 

 to which the solution of a particular salt can be supersaturated. 

 In the case of the alums, for instance, solutions containing salt 

 equivalent to 15 per cent supersaturation may be handled with- 

 out causing precipitation, but on the other hand the change 

 of solubility with temperature is fairly large. Practically, 

 therefore, a temperature difference of 0.3° to 0.5° was found 

 to give good growth. 



With other materials, however, this difference might be too 

 large and if so there would result a period of excessive growth, 

 or a shower of volunteer crystals that would ruin the crystals 

 being developed. No measurement of the actual rate of transfer 

 of solution from one thermostat to the other was made. The 

 rate of stirring must obviously be kept constant while crystals 

 are being grown. If the room in which the apparatus is placed 

 is subjected to large temperature fluctuations it is necessary 

 to maintain the temperature of the water in the cooling coils 

 at the same temperature as that of the crystallizer. 



The course of the circulating solution is as follows: The 

 solution comes into the saturator through tube (R), flows over 

 the heating lamp (H), the hot stream striking the feeding crystals 



