406 Correspondence of J. Nickles. 
Still, this apparatus presented a great fault, viz: the difficulty of main- 
taining the vacuum: not bei 
__ Stones covered with coal tar, or even with a greasy or resinous coating, 
resist the action of wind bringing salt spray from the sea better than do 
r. Kuhlman saw a striking example of this in the Bay of Biscay 
upon a building erected in 1858. Upon the more exposed points, the 
with oil, the parts covered by the color have been so protected from 
ter, becoming anhydrous, is thoroughly penetrated by the tarry matter, 
ture of 400°C. At from 150° to 200° C., stearic acid acts like resin ; 
the plaster becomes impregnated with it, and at the same time loses its 
water of hydration, which is recognized from the boiling which it occa- 
sions in the bath. 6 
_ With liquids which do not wet the plaster, this penetration does not 
take place. Mr. Kuhlman has tried in vain to effect it with melted sul- 
hur or with mereu 
| nercury. oe ee ee 
tit is not only water which can be displaced by coal tar; other 
es are similarly affected: e. g., crystallized peroxyd of manganese 
