MECHANICS AND USEFUL ARTS. 67 



well as mantel-pieces and jambs, which, without any coloring- 

 matter, present a neat and stone-like appearance. 



It is remarkable that the peculiar odor of the gas-lime is no 

 longer to be detected when the cement has set. The sulphur 

 compounds are oxidized rapidly, and some of the adhesive quali- 

 ties of the cement are no doubt due to the formation of calcium 

 sulphate or plaster of Paris throughout the mass of the material 

 in the process of hardening. A rubble-wall can be built up and 

 plastered over to resist the action of water in the interval of a 

 tide, as the properly prepared cement will set even under water. 

 The latter property has induced Mr. Prideaux to propose its use 

 for building sea-walls. 



A number of houses in Sheffield, where trial has been made of 

 this material, have been visited and inspected since its first 

 application to walls, floors, and hearthstones, now about 12 

 months ago, and time only appears to tell in favor of its dura- 

 bility. 



PRESERVATION OF CAST-IRON WATER-PIPES. 



In 1858 the cast-iron pipes carrying the Cochituate Water from 

 Boston to South Boston were treated with a preparation from coal 

 tar, known as Dr. Smith's process, and the result has been so 

 favorable that it has been permanently adopted by the Cochituate 

 Water Board, and by the managers of other water works through- 

 out the country, where the materials used for pipe is cast iron. 

 The pipes laid in 1858 were taken up and examined after 10 

 years 1 use, and were found nearly free from rust or ochrous accre- 

 tions. This coal-pitch varnish is applied substantially accord- 

 ing to Dr. Smith's process, which is described as follows in the 

 specifications : 



Every pipe and casting must be entirely free from dust, sand, 

 or rust, when the varnish is applied. 



The varnish or pitch is to be made from coal tar, distilled until 

 all the naphtha is removed, the material deodorized, and the 

 pitch reduced to about the consistency of wax or very thick mo- 

 lasses ; pitch which becomes hard and brittle when cold will not 

 answer for this use. 



Pitch of the proper quality having been obtained, it must be 

 heated in a suitable vessel, to a temperature of 300 Fahrenheit, 

 and must be maintained at not less than that temperature during 

 the dipping. As the material will deteriorate after a number 

 of pipes have been dipped, fresh pitch must be frequently added, 

 and at least 8 per cent, of heavy linseed oil must be added daily 

 with the fresh pitch, and the vessel must be entirely emptied of 

 the pitch and refilled with fresh material as often as may be nec- 

 essary to insure the perfection of the process. 



Each casting shall be kept immersed from 30 to 45 minutes, 

 or until it attains the temperature of 300 Fahrenheit, and, if 

 required by the engineer, shall be heated to such temperature as 

 he may designate before it is dipped. 



After the bath is completed, the castings will be removed and 



