530 



Mr. Charles Tomlinson on 



[Dec. 20, 



crystallizing : the paper became wet and sodden, and all appearance of 

 drops ceased. 



All the solutions thus exposed in drops are more or less affected by the 

 state of the atmosphere as to moisture. The drops of the solution of 

 alum instead of becoming solid in a short time, as they do when the air 

 is dry, remain for hours in the liquid state, and then one or more of them 

 would display an octahedral crystal in the midst of the liquid, which 

 was the more conspicuous in a compound drop, or one made up of five or 

 ten single drops. In damp weather I have known the drops to remain 

 liquid during from twelve to twenty hours ; and I have no doubt that in the 

 damp days of winter this solution, as well as that of other salts, will not 

 be so ready to crystallize as the drops were during the months of June, 

 July, and August, when these experiments were made. 



Drops of sodic sulphate in my bedroom crystallized some of them im- 

 mediately, and all after a few hours. But in a damp air, after heavy 

 rain, the time was considerably extended. I have even found them to 

 remain liquid much longer on paper than on glass. On the other hand 

 I have found magnesic sulphate solidify more readily on paper than on 

 glass, and plumbic acetate and zincic acetate more readily on glass than 

 on paper. But the facility with which the drops solidify on various 

 surfaces seems to vary from day to day ; and hence it does not appear 

 possible to tabulate the salts in the order of their sensitiveness, seeing 

 that the order of one day, or even of one hour, may be quite different 

 from that of another day or hour. Thus on two different days in 

 August equally fine, only on one day the wind was in an easterly, and on 

 the other in a westerly quarter, the order in which the solutions respec- 

 tively crystallized was as follows : — 



Wind easterly. Wind westerly. 



1. Sodic sulphate. 1. Alum. 



2. Sodic acetate. 2. Magnesic sulphate. 



3. Alum. 3. Zincic sulphate. 



4. Magnesic sulphate. 4. Sodic sulphate. 



5. Zincic sulphate. 5. Zincic acetate. 



6. Zincic acetate. 6. Plumbic acetate. 



7. Plumbic acetate. 7. Sodic carbonate. 



8. Sodic carbonate. 8. Sodic acetate. 



The following Table shows the order of crystallization during a 

 southerly wind on a day in August, when heavy showers occurred with 

 intervals of bright sunshine : — 



1. Sodic sulphate crystallized within a few minutes on glass, and some- 



what later on paper. 



2. Ammonia alum : the large drop and several of the small ones were 



covered immediately with minute octahedra ; the action was more 

 rapid on glass than on paper. 



