PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 559 



How TO Test the Presence of Lead in Water. 

 A veiy ready test for lead in water consists in taking two tum- 

 blers, and filling one with water which is known not to have been 

 in contact with lead ; the other being tilled with the suspected 

 water. Dissolve in each about as much bichromate of potash a« 

 will stand on a dime. By daylight the water in each tumbler v/ill 

 be of the color of pale sherry and water. Cover the tumblers so 

 as to keep out dust, and let them stand in a warm place in a room 

 with a fire in it for twenty-four hours. If the suspected water be 

 free from lead, it will have the same color as the other ; but if 

 there be lead in the water, it will have a more or less opalescent 

 tint, as if a drop or more of milk had been put into it. If there 

 be a great quantity of lead in the water, a very slight film of lead 

 will be deposited on the glass. 



Glue. 

 Powdered chalk added to common glue strengthens it. A glue 

 which will resist the action of water is made by boiling one pound 

 of glue in two quarts of skimmed milk. 



Prepared Liquid Glue. 



Take of best white glue sixteen ounces ; white lead, dry, four 

 ounces ; rain water, two pints ; alcohol, four ounces. With con- 

 stant stirring, dissolve the glue and lead in the water by means of 

 a water bath. Add the alcohol, and continue the heat for a few 

 minutes. Lastl}^ pour into bottles while it is still hot. 



Marine Glue. 

 Dissolve three parts of India rubber in thirty-four parts of coal 

 lar naptha — aiding the solution with heat and agitation ; add to it 

 sixty-four parts of powdeiv d shellac, which mnst be heated i;: the 

 mixture till the Avhole is dissolved. While the mixture is hot it 

 is poured upon metal plates in sheets like leather. When required 

 for use, it is heated in a pot till soft, and then applied with a brush 

 to the surfaces to be joined. Two pieces of glue joined with this 

 wood can scarcely be sundered. 



News for Tobacco Smokers. 



The Count De la Tour Dupin has given a valuable hint to 



tobacco smokers. It is a current opinion that the most expensive 



tobaccos contain the least nicotine ; and the Count gives us a plan 



by which a man may smoke cajpoml and only get the effects of the 



