534 S. Tdber — Growth of Crystals. 



in a saturated solution ; two of the crystals being covered by 

 light glass plates while the other two were left uncovered. 

 The crystals were measured from time to time and the results 

 tabulated as before. These results are in every way similar to 

 those obtained in the previous experiments. 



In the fall of 1914 the writer of the present paper began a 

 series of experiments with the object of determining whether 

 it is possible for growing crystals to exert a linear pressure, 

 and if so, the conditions under which the pressure is developed ; 

 for, obviously it is not always in evidence, or such contradic- 

 tory results as those cited above would never have been 

 obtained by careful investigators. Some of the more important 

 experiments conducted by the writer are described in the fol- 

 lowing pages, and the conclusions that may be drawn from 

 them are also discussed. All of the questions growing out of 

 this work have not been solved, but it was thought best to put 

 on record such facts as have been established in order that 

 others might aid in carrying on the investigation. 



Before going into details it is advisable that the problem be 

 clearly defined, for some observers have wrongly attributed to 

 crystal growth certain phenomena that are without question 

 due to other processes. Reference is here made to that class 

 of phenomena which are due to chemical or physical changes 

 taking place with increases of volume in a closed and insuf- 

 ficient space. The present investigation has been limited to 

 those evidences of mechanical pressure accompanying crystal- 

 lization that are not obviously to be explained in this way. 



The writer began his investigations by growing crystals of 

 alum in crystallizing dishes placed in desiccators containing 

 sulphuric acid, care being taken to follow all of the precautions 

 observed by Bruhns and Mecklenburg. The experiments were 

 conducted in a room where the temperature fluctuations were 

 not more than 5° C. Some of the crystallizing dishes con- 

 tained both loaded and unloaded crystals, while other dishes 

 contained only loaded crystals ; otherwise the conditions were 

 the same for all of the tests. At first the results were rather 

 confusing, some crystals lifting their load several tenths 

 of a millimeter, while others showed no increase in height. 

 Later it was found that the loaded crystals were able to increase 

 in height only when there were no unloaded crystals present in 

 the same crystallizing dish. If unloaded crystals were placed 

 in the crystallizing dish with a loaded crystal, or if volunteer 

 crystals began to form soon after the experiment was started, 

 then the loaded crystal did not show any increase in height, 

 and in many cases there was an actual decrease in height. 



Confirmatory experiments were made using other salts, such 

 as copper sulphate and potassium sulphate, instead of alum. 



