ON IMPROVING THE QUALITV OF SAWS. 243 



mongers' shreds, one gallon per 28 oz. ; and parchment cuttings, 

 one gallon per 50 (xz.. 



The exact quantity of water ought first to he put into the boiler, 

 according to the quantity of size intended to be made ; and when 

 the article to be boiled into size, is added, the depth, or quantity 

 of liquid required to be constantly maintained till the gelatine is 

 extracted by the boiling, will he correctly ascertained ; and any 

 visible waste occasioned in the boiler during the operation, must 

 be continually supplied, by adding the necessary quantity of water ; 

 or otherwise considerable time will be lost in the process. 



An iron pan, or boiler, is much better than any other, provided 

 that care is taken to add cold water, by a little at a time, while the 

 boiling is continued. And it is also necessary to have an iron 

 grating placed inside the boiler, in order to prevent the article 

 from burning to the bottom of it, and to lessen the time and trouble 

 required in frequently stirring it. 



We have extracted the above useful particulars from the Manu- 

 facturer''s Assistant, a work containing much valuable information ; 

 to which we may also add, that, after the boiling is completed, the 

 clear size ought to be strained from the dregs, To finish it for use. 

 And that the paper-hanging manufacturers prefer to make their 

 white size for light colors, of the skin which covers the foreheads 

 of calves, previously freed from the hair by liming them. The 

 skins of soles, and no doubt of other fishes also, after being freed 

 from all greasiness by soaking them in lime-water, will very readi- 

 ly dissolve into a size in water, by the assistance of heat ; and 

 which, after straining it clear, may no doubt be usefully employed 

 for many of the purposes of isinglass, &;c. [Tech. Repository. 



On Improving the Qualitij of Sarvs, by Hammer-hardening their 



Teeth. 



The Editor lately mentioning to Mr. Christie, the worthy Secre- 

 tary of the London Mechanics Institution, Mr. Turrell's great im- 

 provement in gravers, eflfected by hammer-hardening them ;, it oc- 

 curred to him, that the practice, frequently adopted by smiths, and 

 other workmen, of hammering the worn and blunted lops of the 

 teeth of their back and frame-saws, merely with a view of spread- 

 ing them sideways, so as to free themselves in use, j)revious to 

 filing them sharp again ; must not only have that eHecl, but must 

 likewise greatly conduce to the improvement oi ihc'w hardness and 

 toughness, from the condensing effect of the hammer upon them. 



Mr. J. I. Hawkins, on being informed of this, by the Editor,, 

 perfectly agreed in this opinion of Mr. Christie's ; but, with his 

 usual acuteness, suggested the farther improvement of first filing 

 the teeth into shape, and then finishing Ihern by hammer-hardening 

 their tops ; which would not only spread them out sideways, but 

 would also preserve to them all the advantages of the elfcct of the 

 hammer upon them ; which, according to the present practice of 

 filing them after hammering them, are in a great measure lost ; and 



