OF ARTS AND SCIENCES. 79 



" Pipe employed to conduct Dedham spring water is internally cor. 

 roded, and presents at intervals deep depressions, the result of more 

 extreme local action. Pipe of one well in Cambridge is appreciably 

 corroded. Pipe of wells in Boston is frequently consumed in peri- 

 ods of from si.x to eighteen months. 



" The above results and observations show, that, — 



" 1st. Many well-waters, in a space of time comparatively short, act 

 on lead. This has been fully established by the researches of Dr. 

 Dana* in this country, and by observations in England. 



" 2d. That, except after longer exposure than will ordinarily occur 

 in actual use, the amount of lead coming into solution in Croton, 

 Schuylkill, or Jamaica waters is too small to occasion any solicitude. 



" Plence it may be inferred from the above, and from the great sim- 

 ilarity of Cochituate to Jamaica, Croton, and Schuylkill waters, in its 

 relations to lead, that the quantify of lead that will be dissolved in 

 Cochituate water in actual service will, for all practical purposes, be 

 of no moment. 



" The recognition and quantitative determination of very minute 

 quantities are not always without difficulty ; where many and rapid 

 determinations are required, the processes of gathering upon a filter, 

 washing, drying, igniting, and weighing consume far too much time, 

 and are sometimes less accurate than other and more indirect methods. 

 That which I have employed is based upon the mode of analyzing sil- 

 ver coin proposed by Gay-Lussac,t and adopted quite universally at 

 mints. The same general method has been extended by Gay-Lussac 

 to ascertain the strength of alkalies and bleaching-powder. It is em- 

 ployed with protosulphate of iron and subchloride of mercury for the 

 latter purpose. It is the method of graduated solutions. A gramme of 

 lead in the form of the acetate (common sugar of lead), which contains 

 three atoms of water, is dissolved in 100 grammes or parts of distilled 

 water. This constitutes solution No. 1. Ten parts of this solution are 

 diluted with ninety parts of water to make solution No. 2. Ten parts 

 of solution No. 2, diluted with ninety parts of water, make solution No. 

 3. In the same manner solutions No. 4, No. 5, and No. 6 are prepared. 



" Ten parts of each solution are placed in corresponding test-tubes 

 (about six inches long, five eighths of an inch wide, and closed at one 

 end), and hydrosulphuric acid transmitted through them till the liquid, 



* Appendix to Tanquerel, by Dana. \ Jlnnahs de Cliemie et de Physique. 



