HYDROGEN PEROXIDE 



HYDROPHOBIA 



It finds employment also in dyeing and in the 

 manufacture of dyes, in the treatment of bones 

 for the production of glue, gelatin and bone- 

 black, and in many other industrial processes. 

 Sec HYDROGEN ; CHLORINE. J J.S. 



HYDROGEN PEROXIDE, per ox' id, also 

 known as HYDROGEN DIOXIDE, PEROXIDE OF HY- 

 DROGEN, or OXYGENATED WATER, is a compound 

 of oxygen and hydrogen containing twice as 

 much oxygen per pound of hydrogen as does 

 water. Beca\ise it contains more oxygen than 

 the normal compound water, it is very un- 

 stable, easily giving up oxygen and becoming 

 water. Oxygen so set free is called nascent 

 (newborn), and is very active chemically, 

 uniting easily with other substances with which 

 it comes in contact; for instance, black lead 

 sulphide is oxidized to white lead sulphate 

 (sec OXIDATION). This property makes it valu- 

 able as an antiseptic in medicine, and as a 

 bleaching agent, especially for hair, feathers 

 and ivory, which are injured by cheaper 

 bleaching agents. Hydrogen peroxide is com- 

 monly sold as a three per cent solution in 

 water. The pure substance is rarely made. 

 It is a colorless liquid, heavier than water, and 

 is difficult to keep on account of its tendency 

 to decompose. J.F.S. 



HYDROGEN SULPHIDE, sul'fide. See SUL- 

 PHURETED HYDROGEN. 



HYDROGRAPHY, hidrog'rafi, that branch 

 of physical geography which treats of the sur- 

 face waters of the earth. It is concerned with 

 determining and making known the condition 

 and depth of navigable waters, both oceanic 

 and inland, and the making of charts and maps 

 showing the coast formation, channels, reefs, 

 rocks, and also currents, tides and winds. The 

 United States coast and river surveys are con- 

 ducted under the direction of the Hydrographic 

 Department at Washington. This service is 

 very important to the commercial and marine 

 interests of the country. Great Britain, being 

 a maritime nation, has a very thorough and 

 extensive governmental department of hydrog- 

 raphy, and this service for Canada has always 

 been volunteered by Britain. 



HYDROMETER, hi drom' e ter, an instru- 

 ment to determine the density of liquids. It 

 consists usually of a slender sealed glass tube 

 with a bulb at one end containing mercury or 

 shot, but may have a cup at the end to hold 

 the weight. The weight is required to hold 

 the instrument in a vertical position in the 

 liquid. The depth to which the instrument 

 sinks in water is marked zero, and the rest 



of the stem is scaled like a thermometer. In 

 any liquid other than water it sinks to a depth 

 greater or less than it would in water; the 

 density of the liquid 

 may thereby be read. 

 Hydrometers used to 

 test the purity of 

 milk are called lac- 

 tometers; of alcohol, 

 alcoholometers; and 

 the strength of the 

 brine in the boilers 

 of seagoing ships, 

 salinometers. See 

 GRAVITY, SPECIFIC. 



HYDROPHOBIA, 

 hi dro fo'bi o, a dread 

 disease, the name 

 of which means 

 jear of water. It re- 

 sults from the bite 

 of a mad dog or 

 other animal suffer- 

 ing from hydropho- 

 bia, and first shows 

 itself by inability to 

 swallow, not only 

 water but even the 

 secret ions of the 

 mouth; unless prog- 



- of the malady 

 is arrested convul- 

 sions and death fol- 

 low. It is now pos- 

 sible to save the 

 victim by use of 

 Pasteur treatment, 

 which is available all 

 over the civilized 

 world, but which 

 should be used im- 

 mediately after the 

 accident ; once the 

 disease develops the treatment is valueless. 

 The period of time elapsing between the bite 

 and the convulsions is so variable (from one 

 week to two years) that the Pasteur treatment 

 should be used in every suspected case, inas- 

 much as cases so treated rarely develop the 

 disease. 



Treatment. When a person is bitten, the 

 victim should suck the wound, if possible, and 

 hasten to the nearest physician, who will 

 promptly burn the wound with a hot iron or 

 nitric or carbolic acid. Then the patient 

 should be taken at once to the nearest place 



HYDROMETERS 



(a) Beaume's hydrometer. 



(b) Nicholson's hydrome- 



ter. 



