Thickness in parts of an inch.

Of the Weight of a Superficial Foot of Plate or Sheet Iron, Copper, and Brass, in pounds.

Note. No. 1 wire gauge equal 5ths of an inch.

The great variety of thicknesses into which copper is manufactured, cause in trade the weight to be named whereby to determine the thickness required, the unit being that of a common sheet, so designated, viz. 4 feet by 2 feet, in lbs., thus:

A 70 lb. plate isths of an inch in thickness.

461

66

"

The thickness of lead is also in common determined or understood by the weight, the unit being that of a square or superficial foot; thus:

4 lbs. lead is th of an inch in thickness.

6

66

1. Suppose I have an article of plate iron, the weight of which is 728 lbs., but want the same of copper, and of similar dimensions, what will be its weight?

728 x 1.16844'48 lbs."

2. A model of dry pine, weighing 324 lbs., and in which the iron for its construction forms no material portion of the weight, what may I anticipate its weight to be in cast iron?

32.5 x 16 = 520 lbs.

Note. It frequently occurs, in the formation or construction of models, that neither the quality nor condition of the timber can be properly estimated; and, in such cases, it may be a near enough approximation to reckon 15 lbs. of cast iron to each lb. of model.

SILVERING POWDER, &c., for silvering copper, covering the worn parts of plated goods, &c.-1. Nitrate of silver 30 gr., common salt 30 gr., cream of tartar 34 dr. Mix. Moistened with water, and rubbed on dial plates or other copper articles, it coats them with silver.

2. Silver precipitated from its nitric solution by copper 20 gr., alum 30 gr., creain of tartar 2 dr., salt 2 dr.

3. Precipitated silver oz, common salt 2 oz., muriate of ammonia 2 oz., corrosive sublimate 1 dr. Make it into a paste with water. Copper utensils are previously boiled with tartar and alum, and rubbed with this paste, then made red hot, and afterwards polished.

4. Dissolve muriate of silver in a solution of hyposulphite of soda, and mix this with prepared hartshorn, or other suitable powder.

PLATINA FOR SPRINGS.-Platinum 1 part; gold 12 parts. Add the platinum to the gold in a state of fusion.

Strength of Journals of Shafts.

Mr. Buchanan's rule is: The cube root of the weight in cwts. is nearly equal to the diameter of the journal; it being prudent to make the journal a little more than less, and to make a due allowance for wearing.

Ec. What is the diameter of a journal of a water-wheel shaft, 13 feet long, the weight of the wheel being 15 tons?

By Mr. B.'s rule,

3/15 × 20=67, or 7 inches diameter.