SQd TRANSACTIONS OF THE AMERICAN INSTITUTE. 



With these hurried allusions to the nature of sewage matter to be dis- 

 posed of, its analysis, its utilization, the principles which govern the 

 arrangement of sewers, the comparative merits of pipes, and the sanitary 

 evils to be remedied, this subject is commended to the earnest consideration 

 of the members of the Polytechnic association, as pertaining to a matter 

 of vital public welfare and of scientific research. 



At the conclusion of the reading of this valuable paper, "The Manufac- 

 ture of Combs " was selected for the next discussion, when the association 

 adjourned. 



• American Institute Polytechnic Association, ] 

 Jpril 2T, 1865. j 



Prof. Samuel D. Tillman, in the chair; Mr. Benjamin Garvey, Secretary. 



Metals — Solid and Melted. 



Dr. Rowell gave an account of some experiments which he had made to 

 test the relative specific gravity of solid and molten lead. He took a 

 hydrometer tube, which is a glass tube with two bulbs blown in it, a small 

 one at the bottom and a larger one above, and introducing a small quantity 

 of lead he melted the metal with an alcohol lamp. The quantity of lead 

 was sufficient to fill the lower bulb and half the upper bulb. Dr. Rowell 

 supposed that if the metal shrank in hardening it would draw the two 

 bulbs together and break the glass at the neck, while if it expanded it 

 •would burst the lower bulb. The glass was not broken; he, therefore, con- 

 cluded that lead in hardening neither expands nor contracts, at all events 

 not more than glass. 



Another experiment resulted in the same conclusion. Having a kettle 

 with a hemispherical bottom he filled it with molten lead and allowed it to 

 cool. He then melted it all except a little lump at the center of the sur- 

 face, and observed that the upper part of this lump was precisely at the 

 level of the surface of the molten mass. But if the temperature of the 

 molten lead be raised a few degrees above the melting point, the solid lump 

 sinks; lead, whether molten or solid, being subject to the law of expansion 

 like other bodies. 



The case is different with iron. Visiting an iron foundry a few days 

 before, he took the opportunity to drop a small ball of nearly red hot cast- 

 iron into a ladle of the molten metal, and the ball floated with about one- 

 tenth of its mass above the surface. One of the workmen dropped a leaden 

 bullet into the ladle, when it went to the bottom instantly. 



Mr. Blanchard said that he had tried the experiment of throwing solid 

 cast-iron into molten cast-iron a thousand times, and it will always float. 



Mr. Norman Wiard observed that there was some deception practiced in 

 relation to the lead bullet; as every foundry man knows that if lead be 

 mixed with molten cast-iron an explosion follows. The iron may all be 

 thrown out of a ladle at any time by placing a little lead in the bottom of 

 the ladle before the iron is drawn in. 



Mr. Bird said that in melting lead he had tried the experiment many 



