18J0.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



.300 



lead or wliite lead is not to be recommended ; for the oxides of lead are, all 

 of them, especially the second, very easy of decomposition when mixed with 

 oil and heated. While decomposing, that is, while the oxygen of the lead is 

 combining with the combustible ingredients of the oil, a considerable increase 

 of heat is excited, and this may, under favourable circumstances, be so great 

 as to produce actual combustion of the oil. 



In making experiments with the intention of discovering a composition free 

 from the objections to oU paint, and at the same time cheap, the following 

 occurred to me, and I liud on trial that it adheres perfectly well when dry to 

 the surface of iron, and will bear a heat of between 500° and 600° without 

 material injury ; it also retards considerably the efflux of heat, and will there- 

 fore, I think, be found a very good protection for the felt. It is made as 

 follows :^ 



Take very stiff clay and sand (that of a bright yellow colour is best), dry 

 them separately at a heat not much exceeding that of boiling water ; reduce 



them to powder and pass them througli a moderately fine sifve. Of the sond 

 take four measures, and of the clay two measures, and mix tliem well ; then 

 add one measure of linseed meal, and one measure of horse dung, mixing them 

 with the other ingredients as accurately as possible. Pour into any con- 

 venient vessel boiling hot water, and shake into it the above composition by 

 small quantities at a time, observing that the last added quantity is thoroughly 

 soaked Iiefore another is jjut in ; there will thus be obtained a slippery semi- 

 gelatinons mass whicli is best applied to the surface of the boiler by means of 

 a trowel. 



The first layer snould be very thin, ami care must he taken that it does not 

 slip down while wet, when it has become dry it will adhere firmly, and if its 

 surface is left ratlier rough, the second layer may be applied without any 

 hazard of its slipping. 



A. AlKIN. 



7, Bloomsbury Square, Aug. 6, 18-10. 



TABLE No. T. 



Dttail of Coals consumed and water evaporated in the course of 72 experiments, daring which there were 4275 bushels of coals consumed, 1287 tons and 



8 cvvts. of water evaporated. 



