HYDRODYNAMICS.

Water, considered from a chemical standpoint, is a compound substance consisting of hydrogen and oxygen, in the proportion of two volumes of the former gas to one volume of the latter; or by weight it is composed of two parts of hydrogen united with sixteen parts of oxygen. It should be noted that the union of these two gases is effected by chemical action and not by mechanical mixture. Pure water is transparent, inodorous and tasteless.

Under ordinary conditions water passes the liquid form only at temperatures lying between 32° F. and 212° F.; it assumes a solid form, that of ice or snow at 32° F., and it takes the form of vapor or steam at 212° F.

There are four notable temperatures for water, namely:

32° F.,	or	0° C.	= the freezing point under one atmosphere.
39°·1	or	4°	= the point of maximum density.
62°	or	16°·66	= the standard temperature.
212°	or	100°	= the boiling point, under one atmosphere.

The temperature 62° F. is the temperature of water used in calculating the specific gravity of bodies, with respect to the gravity or density of water as a basis, or as unity.

Weight of one cubic foot of Pure Water.

At 32° F.		= 62·418	pounds.
At 39°·1.		= 62·425	„
At 62°	(Standard temperature)	= 62·355	„
At 212°		= 59·640	„

The weight of a cubic foot of water is, it may be added, about 1000 ounces (exactly 998·8 ounces), at the temperature of maximum density.

The weight of a cylindrical foot of water at 62° F. is 48·973 pounds.

Weight of one cubic inch of Pure Water.

At 32° F.	= ·03612	pound,	or	0·5779	ounce.
At 37°·1	= ·036125	„	„	0·5780	„
At 62°	= ·03608	„	„	0·5773	„	or 252·595 grains.
At 212°	= ·03451	„	„	0·5522	„

The weight of one cylindrical inch of pure water at 62° F. is ·02833 pounds, or 0·4533 ounce.

Volume of one pound of Pure Water.

At 32° F.	= ·016021	cubic foot,	or	27·684	cubic inches.
At 39°·1	= ·016019	„	„	27·680	„
At 62°	= ·016037	„	„	27·712	„
At 212°	= ·016770	„	„	28·978	„

The volume of one ounce of pure water at 62° F. is 1·732 cubic inches.

The weight of water is usually taken in round numbers, for ordinary calculations, at 62·4 lbs. per cubic foot, which is the weight at 52°·3 F.; or it is taken at 62¹⁄₂ lbs. per cubic foot.

Salt water boils at a higher temperature than fresh water owing to its greater density, and because the boiling point of water is increased by any substance that enters into chemical combination with it. The density of water decreases as the temperature increases, since heat destroys cohesion and expands the particles, causing them to occupy greater space, where precision is not required; the pressure on a square foot at different ocean depths are approximate, in the following

TABLE.

Depth in feet.	Pressure on sq. foot.
8	500	lbs.
16	1000	„
24	1500	„
32	2000	„
40	2500	„
48	3000	„
56	3500	„
64	4000	„
72	4500	„
80	5000	„
88	5500	„
96	6000	„
1 mile, or 5,280 feet,	330,000 lbs.
5 miles,	1,650,000 „

This table is based upon an allowance of 62¹⁄₂ lbs. of water to the cubic foot, thus 8 feet × 62¹⁄₂ = 500, etc.