74 ANNUAL OF SCIENTIFIC DISCOVERT. 



beautiful, granulated, velvet-like surface of the field, upon which 

 the polished portions appear to rest, is produced by the acid only, 

 without the application of any tool. 



The bronzing, the final stage of the manufacture, is thus accom- 

 plished : The iron, covered with a film of vegetable oil, is ex- 

 pftsed to a high temperature, previously determined by experi- 

 ment, and thus the desired color is obtained through the union of 

 the carbonized oil with the oxidized metal. This is a permanent 

 bronzing, since it is actually incorporated with the substance of 

 the metal, and consequently not liable to injury from the action of 

 the atmosphere, the touch of the hand, changes of temperature, 

 excessive dampness, and similar casualties. Mech. Mag., July, 

 1867. 



BIRKHOLS' METAL. 



The following is the copy of the patent, describing the process 

 for making this valuable composition, resembling brass, securing 

 great strength and solidity : 



" Be it known that I, Alexander Birkhols, of the city and county 

 of Hartford, and State of Connecticut, have invented or discovered 

 certain new and useful improvements in the composition of cast 

 metal, by means of which greater strength is acquired ; and I do 

 hereby declare that the same is described in the following speci- 

 fications. 



"So as to enable a person skilled to make the same, I will there- 

 fore proceed to describe its component parts, the essential in- 

 gredient of which is cast iron. To make 100 pounds of this com- 

 position, I. first take 2 pounds of cast iron, 2 ounces of charcoal, 

 put into a crucible and heat to a white heat ; I then add thereto 

 60 pounds of copper. Heat till both are melted together, then 

 add 4 ounces of borax and 38 pounds of zinc. 



" The mode of proceeding during the melting is much the same 

 as with all other metals melted in crucibles. When melted it 

 may be poured into moulds or bars suitable for the forge or roll- 

 ing mill. Its strength is estimated to be 8,000 pounds greater tQ 

 the square inch than the best wrought iron, rendering it far more 

 valuable for various purposes. 



" The proportion of parts may be varied, which will only change 

 proportionably the desired effect, namely, greater amount of 

 strength and solidity ; but I believe that the proportions about as 

 described will be best for all practicable purposes. I have de- 

 scribed its component parts and the mode of proceeding to pro- 

 duce my improved composition, so as to enable a person skilled 

 to make the same. 



'* What I claim, therefore, and desire to secure by letters patent, 

 is the introduction of cast iron into a composition composed of 

 copper and zinc in about the proportion, substantially in the man- 

 ner as described." 



COLORING OF ZINC PLATES. 



A variety of beautiful colors, corresponding to those of the 



