ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



719 



I E is a rubber cork through which passes the tube T which terminates 

 in a cup-shaped expansion C. B is a glass float, the upper end of which 

 closes T when it rises, and drops into A when it descends. A is a cup 

 with a tube dipping into the mercury. When the apparatus is in work, 

 the heat causes the mercury to rise into the cup A, so that the float B 

 ascends into the tube T, thus cutting off the gas supply. The form of 

 the right-hand figure is serviceable for only one temperature, but by 

 interposing a metal cap and screw (as shown in the left-hand figure) 

 acting on a leather diaphragm, the apparatus may be regulated for any 

 temperature. 



Fig. 169. 



Birge's Cone Net.* — E. A. Birge describes how to make a cone- 

 shaped net for collecting small aquatic organisms, and B. H. Wolcott 

 describes some modifications which have served to render this apparatus 

 more useful. For the details ot the construction the original should be 

 consulted. 



Raising the Melting-point of Gelatin by means of Formalin.! — 

 Dr. H. J. van't Hoff found that the addition of formalin raises the melt- 

 ing-point of gelatin. The addition of 1 to 1750 produces a gelatin 

 which liquefies in a water-bath at 40", while in the proportion of 1 to 

 500 (1 drop of 40 p.c. formalin to 10 grin, gelatin) the mass retains its 

 solidity in boiling water. 



* Journ. Applied Microscopy, iv. (1901) pp. 1405-9 (7 figs.). 

 t Centralbl. Bakt., !«• Abt, xxx. (1901) p. 36S. 



