126 



Mr. J. G. Grenfell on 



[June 15, 



dusty corners of the shelves, on paper, on every place and kind of sur- 

 face I could find : remained liquid in all cases. 



8. Spread a number of drops of the same on a glass plate, covering 

 nearly the whole oE it. Made about half crystallize. Left them exposed 

 for three days ; they remained liquid, though the normal salt effloresces 

 slightly. 



9. Ammonia alum : many drops on a glass plate ; they formed films 

 by evaporation ; made a good many crystallize, when they broke open, 

 early in the day : carried them out in a high ^ wind to the house of a 

 neighbour, and brought them back ; then late at night put a number of 

 fresh drops on the plate, and several of them remained liquid all night. 



10. Sodium carbonate is not affected by any surface in my laboratory. 

 I have spread a drop over a dirty glass plate so as to cover a good many 

 square inches, and it slowly evaporated, giving crystals. Drops on the 

 floor, shelves, bottles, &c. of the laboratory invariably remain liquid. 



I could give many other instances, but these are sufficient to show that 

 the air does not ordinarily contain these salts, and that it does not readily 

 catch them up and deposit them on all kinds of surfaces ; and yet 

 these salts are remarkably sensitive to crystals of the same kind. The 

 effect of using cotton-wool is a good example of this. Another is this : — 

 Touched a crystallized drop of sodium acetate with a pin ; passed the 

 pin repeatedly through my coat : active at once. After touching a 

 crystal the finger needs to be washed carefully. Again, sodium sulphate 

 crystallizes almost invariably on any dirty surface in my laboratory, and 

 ammonia alum generally. Even the sodium acetate crystallizes at times 

 when I am at work with the same salt close by. 



Sodium sulphate crystallizes generally on a clean plate exposed in my 

 laboratory as 10-atom salt, whilst if protected by an inverted beaker it 

 dries up by evaporation, forming the modified salt. So, again, I have had 

 two drops of sodium sulphate liquid all night, and both crystallize within 

 ten minutes of my entering the room in the morning. In my bedroom, 

 however, I left a test-tube containing this solution open all night with 

 the pipette on the mantlepiece. In the morning the solution had not 

 crystallized, while the end of the pipette was covered with a white 

 incrustation, which was inactive in the liquid. The incrustation was 

 again left to dry up, and then contained plenty of water, being evidently 

 the 7-atom salt. 



Tor sodium acetate and carbonate it is quite useless to have any cover on 

 the flask or test-tube which contains them, and also for the sulphate in an 

 ordinary room. Care must be taken that crystals are not formed near the 

 mouth of the tube, so as to fall in ; but that is the only precaution neces- 

 sary. Carbonate of soda by evaporation becomes oily like sodium and 

 potassium acetates. I have not yet investigated the composition of the 

 films and crystals which these solutions deposit. 



Normal sodium acetate when heated leaves a white mass which deli- 



