Paste. — Soldering Sheet Iron, 379 



and mixed with warm water to a proper consistence. A 

 pound of potatoes will make a quart of good yeast. Keep 

 it moderately warm by fermenting. This recipe is in sub- 

 stance from Dr. Hunter, who observes that yeast so made 

 will keep well. No sugar is used by bakers when adding 

 the pulp of potatoes to their rising. — Yorkshire Gazette. 



11. Paste. — Dr. McCulloch, in a paper on the power of 

 perfumes in preventing mouldiness, gives the following di- 

 rections for the preparation of a paste, which, as it will keep 

 any length of time, and is always ready for use, may be of 

 great service to mineralogists and others. " That which I 

 have long used in this manner is made of flour in the usual 

 way, but rather thick, with a proportion of brown sugar, 

 and a small quantity of corrosive sublimate. The use of 

 the sugar is to keep it flexible, so as to prevent its scaling 

 off from smooth surfaces; and that of the corrosive subli- 

 mate, independently of preserving it from insects, is an ef- 

 fectual check against its fermentation. This salt, however, 

 does not prevent the formation of mouldiness ; but as a 

 drop or two of the essential oils above mentioned, (lavender, 

 peppermint, anise, bergamot, Sic.) is a complete security a- 

 gainst this, all the causes of destruction are effectually guard- 

 ed against. Paste made in this manner and exposed to the 

 air, dries without change to a state resembling horn, so that 

 it may at any time be wetted again, and applied to use. 

 When kept in a close covered pot, it may be preserved in 

 a state for use at all times." — Edin. Jour. viii. 35. 



12. Soldering Sheet Iron. — Sheet iron may be soldered by 

 means of filings of soft cast iron applied with borax depri- 

 ved of its water of crystallization and sal ammoniac. Tubes 

 of sheet iron have been constructed at Birmingham lately 

 by means of a process of this kind, which according to Mr. 

 Perkins and Mr. Gill is to be practised in the following 

 manner : — The borax is to be dried in a crucible, not till 

 it fuses, but till it forms a white crust ; then powdered, and 

 mixed with the iron filings : the joint is to be made bright, 

 and moistened with a solution of the sal ammoniac ; then 

 the mixture is to be made into a thick paste with water ; 

 and placed along the inside of the joints, and the whole 

 heated over a clear fire till the cast iron fuses. 



Tech. Rep. III. 110. 



