86 ANNUAL OF SCIENTIFIC DISCOVERY. 



and 1.160, the density of the exhausted battery, is divided into 144 parts, by 

 which division every degree represents 1 grain of zinc dissolved in 1000 grains 

 of bulk of fluid. The opposite side of the scale between the same points is 

 divided into 60 parts, each of wliich is for every grain of bulk in the fluid, 

 about T7J L _ of an inch in thickness, for every superficial inch of surface upon 

 which the copper is reduced in the precipitating trough. In this division a 

 little allowance has been made for some local action of the zinc, and by this 

 instrument the quantity of that metal which has entered into combination 

 with the oxygen of the water in which it is subsequently dissolved, is really 

 weighed. In the application of the battery meter we have an illustration of a 

 law which governs all physical phenomena, that without a change of matter 

 we can not have any physical force; for in the electro-metallurgic apparatus 

 we have an effect equal to the original change of matter within a trifling per 

 centage. Thus by the use of the battery-meter, this great law is popularized, 

 furnishing a remarkable illustration of the reference of effect to cause. To 

 contain the battery with its charge the best salt-glazed stone-ware is em- 

 ployed, although no form of earthenware has been yet found permanently to 

 resist the attacks of the metallic saline solution, but being less brittle, it is 

 still preferable to glass. 



The best standard salt for the reduction of copper by electro-metallurgy has 

 been hitherto the sulphate, and, with the occasional exception of the nitrate, 

 is invariably employed. On procuring suitable originals, with proper means 

 of duplication, the next process is to obtain perfect models, gutta percha 

 blackleaded is generally emploj-ed. When perfection is desired, electro moulds, 

 and electro moulds alone, are relied on, for which purpose the original is placed 

 in the depositing trough, and a thick electro mould deposited. The casts are 

 generally deposited so thick in the compound trough that they can be turned 

 down to the required form and size, and all depositions in electro moulds re- 

 quire for the highest perfection the utmost care, and the casts when ready 

 for printing are mounted on solid brass blocks. 



MACHINE FOB MAKING TREE-NAILS. 



The business of making locust tree-nails is an important branch of American 

 industry. Tree-nail is the technical name of a long pin with which the planks 

 of a ship are fastened to the timbers. It is believed by those well acquainted 

 with the business that the best timber in the world for tree-nails is the locust 

 of Long Island. This is an American tree. It has been introduced into 

 Europe, and in, some situations produces excellent timber, while in others it is 

 pronounced worthless. The true variety grows large enough for ship timber, 

 and it has a great tendency to sprout from the roots after the original stalk 

 has been cut away, thus reproducing itself continually. It is the timber of 

 these sprouts, when some six or eight inches diameter and ten to twenty years 

 of age, that is mostly used for the manufacture of tree-nails. 



Tree-nails are usually made by sawing the timber into suitable lengths while 

 in a green state, and splitting up the bolts with a frow. The sticks are then 

 shaved octagonally, and this requires nice work, as they must be very true 



