CHEMICAL SCIENCE. 279 



cake. In this state, while warm, it is quite soft ; but may be soon taken up 

 out of the water and drawn out into longer, or pressed into shorter pieces, 

 or cut, or twisted into fragments, which may again be readily reunited by 

 pressure. 



When the cement is cold, or before, it may be removed from the water 

 and wiped dry, when it is fit for use. 



From a rough experiment I made, there appeared to be a loss of about 

 one-fourteenth of the weight of the materials in making this cement, arising 

 from volatile matter and impurities in the pitch and gutta-percha. 



Properties. This cement is of a black color; when cold, it is hard. It is 

 not brittle, but has some degree of elasticity, which is increased by a slight 

 increase of heat. It appears to be not so tough as gutta-percha, but more 

 elastic. Its tenacity is very considerable, but inferior, if I mistake not, to 

 gutta-percha. It softens when put into water at about 100 Fahr. ; and if the 

 heat is gradually increased, it passes through intermediate states of softness, 

 becomes viscous like bird-lime, and may be extended into threads of indefi- 

 nite length ; it remains in this state, even when exposed for some time, in a 

 crucible, to the heat of boiling water, at 212 Fahr. When heated to about 

 100 Fahr., it becomes a thin fluid. Water appears to have no other action 

 upon it but that of softening it when warm or hot, and slowly hardening it 

 when cold. The cement adheres strongly, if pressed on metal or other sur- 

 faces, though water be present, provided such surfaces be warm. 



My first trials with this cement put it to a very severe test. I used it as a 

 substitute for plumbers' solder in repairing the lead gutters on the roof of 

 my house, which were cracked in several places, and admitted water freely 

 in different places, and also to staunch the leaks in an old common and 

 forcing-pump attached for yielding a supply of water for the use of two 

 houses, and raising it about thirty feet. For these purposes I found it quite 

 effectual. All that was necessary, in the case of the gutters, was to remove 

 with a brush all loose earthy matters from the cracked lead, slightly warm 

 it with a hot iron, then pour the cement in a fluid state on the cracks, so as 

 to cover them on both sides ; then a hot iron was drawn along each edge of 

 the cement so as to soften and bevel it down to the lead, as the cement has 

 intermediate degrees of fluidity, and is thicker or thiner as it is exposed to 

 more or less heat. In its thicker state, it may, perhaps, be better adapted to 

 repair cracks in lead or other gutters ; but a crack in such gutters may be read- 

 ily filled up by taking a piece of the dry, cold cement, and applying a warm 

 but not too* hot soldering-iron, so as to soften the cement on the crack, then 

 melt it on each side and cover it with the cement. The cement will adhere 

 with great ease to the lead, and is far more manageable than any of our 

 common solders. A hole in a gutter could be readily stopped with the 

 cement, and a piece of lead of sufficient size to overlap the hole, say, about 

 one-half of an inch ; cover the lead on both sides with a surface of the 

 cement; press it on the hole: then cover the lead and its edges with the 

 cement, as in puttymg a pane of glass. 



In the case of the common and forcing-pump, it was only necessary to 

 have every part that leaked quite dry, and slightly warm, when a good coat- 

 ing of the cement, in its thick state, was applied, so as completely to cover 



* When the soldering-iron is too hot, and applied to the cement, it decomposes a 

 portion of it, or raises it in a white vapor. When it is of the proper temperature, 

 which is about 130 Fahr., it is merely softened or partially melted. 



