USE OF ZINC IN MARINE BOILERS.

Zinc has been used in marine boilers for many years, but it was not until the publication in 1880 of the report of the Admiralty committee that the use of zinc became general. It has been used in various ways: 1.—Virgin spelter, as imported in oblong slabs of various sizes. 2.—Cast, or remelted zinc. 3.—Cast zinc buttons, generally made from virgin spelter or new clean zinc trimmings. 4.—Zinc spheres. 5.—Rolled zinc blocks, generally 12 inches by 6 inches, and thicknesses varying from ¹⁄₄ inch to 1¹⁄₂ inch, generally with a ¹³⁄₁₆-inch hole in the centre.

It is desirable that close-grained zinc of uniform structure and free from impurities should be used, and rolled zinc appears to meet this want. The wear is entirely confined to the surface. It does not appear to become distorted or broken up. On the contrary, it gradually wastes away till only a slight shred, a sort of skeleton frame work, remains to indicate what it has been.

The primary object in the use of zinc in boilers is the prevention of corrosion, but it has also some effect in reducing the amount of incrustation, and rendering it softer and less adherent.

Table

Showing Amount of Sediment collecting in a steam boiler when evaporating 6,000 gallons per week, of 58,318 grains each.

When a gallon of feed water evaporated to dryness at 212 degrees Fahrenheit, leaves of solid matter in grains:	The amount of solid matter collecting in boiler per week will be:
Grains.	Pounds.	Ounces.
1		13.714
2	1	11.428
3	2	9.143
4	3	6.857
5	4	4.571
6	5	2.285
7	6
8	6	13.714
9	7	11.428
10	8	9.142
15	12	13.713
20	17	2.284
25	21	6.855
30	25	11.426
35	30
40	34	4.571
45	38	9.143
50	42	13.714
55	47	2.285
60	51	6.857
65	55	11.428
70	60
75	64	4.571
80	68	9.143
85	72	13.714
90	77	2.285
95	81	6.857
100	85	11.428
110	94	4.571
120	102	13.714
130	111	6.857
140	120
150	128	9.142
160	137	2.285
170	145	11.428
180	154	4.571