of the so-called Storm-glass* 



101 



Sal- Ammoniac. 



16 drachms in 4 fluid-ounces of distilled water, 

 of room 47°. 



Temperature 



Lower 



Time. 



Upper 



Difference. 



Remarks. 



thermometer. 





thermometer. 







o 



h m 



o 



o 





Boil- 232 



10 40 



Boil- 228 



4 





-ing 



Lamp 

 removed. 



ing 







214 



41 



213 



1 





195 



43 



200 



5 





182 



45 



193 



11 





156 



50 



173 



17 



Crystallization began 



136 



55 



156 



20 



and gradually ex- 



128 



58 



146 



18 



tended from the 



126 



11 



140 



14 



bottom upwards, 



124 



2 



135 



11 



and subsided as the 



120 



4 



130 



10 



two temperatures 



118 



5 



128 



10 



became equal. 



115 



7 



125 



10 





116 



8 



122 



6 





112 



10 



118 



6 





112 



12 



118 



6 





110 



14 



114 



4 





104 



17 



108 



4 





100 



20 



104 



4 





96 



24 



100 



4 





92 



31 



92 









In the sal-ammoniac experiment, the phenomena of crystal- 

 lization are striking and beautiful. Crystals like miniature ferns 

 or fir-trees start up from the bottom ; and just over this minute 

 forest a snow-storm sets in and quickly buries it in a multitude 

 of minute six-rayed stars perfectly sharp and distinct to the naked 

 eye, each radius fringed with spikes of unequal length diminish- 

 ing to the point. The stars descend gently, conveying the noise- 

 less idea of falling snow, and the storm becomes slowly propa- 

 gated upwards until the whole tube is filled with these falling 

 stars, and the lower thermometer is half buried. The heat 

 liberated by the crystals sets currents in motion, and some of the 

 stars struggle to force their way upwards by the axis of the tube. 

 Meanwhile a crust forms on the surface like an inverted forest, 

 the temperatures decline, and, when the difference between them 

 is extinguished, the liquid between the top crust and the mass 

 of snow beneath becomes bright and still. 



I cannot fancy a prettier sight than this exhibited to an audience 

 by means of the oxyhydrogen or electrical lamp. The experi- 

 ment may be prepared for such a purpose, or for any one who 

 wishes to see this beautiful effect in miniature, iu the following 



