731 



HYDROGEN. 



HYDROMETER. 



752 



If it be required to produce hydrogen cheaply, though in a very 

 impure state, it may be readily done by passing steam over iron 

 borings heated to redness in a piece of iron gas-pipe. Under these 

 circumstances the iron is converted into an oxide (Fe 3 4 ), and the 

 hydrogen set at liberty. 



Hydrogen is an element. No amount of pressure causes it to 

 abandon its gaseous condition. When pure, it is colourless, tasteless, 

 transparent, and inodorous. It is the lightest body in nature, being 

 sixteen times lighter than oxygen, and fourteen and a half times 

 lighter than atmospheric air ; its specific gravity is, therefore, 0-0692, 

 air being taken as unity. One hundred cubic inches of it weigh only 

 2'14 grains. 



This gas extinguishes flame ; but when it meets with a supporter of 

 combustion, as oxygen, it burns readily, with a continuous but feeble 

 flame, generating much heat. When mixed with half its volume of 

 oxygen, and the mixture is ignited by a taper, or by throwing into it 

 a small quantity of platinum black, immediate and loud explosion 

 ensues, attended with the formation of water by the combination of 

 the gases ; hence the name hydrogen, or the water-producer, from vSup, 

 " water," and ftwaa. " I generate." It is irrespirable for any length of 

 time, but when inspired for a short period it renders the voice remark- 

 ably but not permanently shrill ; it does not appear to be poisonous, 

 for when mixed with a due proportion of oxygen it may be respired 

 without inconvenience ; when it proves fata], it seems to do so by the 

 mere exclusion of oxygen. 



It is very sparingly soluble in water, 100 cubic inches taking up 

 only about one inch and a half of the gas ; nor is there any other liquid 

 whiclk is capable of dissolving it in notable quantity. Hydrogen, 

 neither in the gaseous state nor in solution, possesses either acid or 

 alkaline properties. In its combinations it is powerfully electro-positive, 

 and chemically plays more the part of a metal than of a metalloid. 



In its separate state, hydrogen has Hot been applied to any very 

 useful purpose ; but on account of its extreme lightness it has been 

 used to fill air-balloons ; at present, however, coal-gas is substituted 

 for aeronautic purposes, by reason of the facility with which it is 

 obtained. This, however, from its greater density, requires much 

 larger balloons than hydrogen gas. 



When mixed with oxygen gas, and the mixture gradually burned in 

 a small jet issuing from such a blowpipe as in described under DRUM- 

 MO^D LIGHT, a temperature is produced sufficiently intense to melt 

 platinum ; and even if burned in the air, the oxygen of which serves 

 as a supporter of combustion, a considerable degree of heat is gene- 

 rated. 



When a very small jet of hydrogen gas is burned, the flickering 

 nature of the flame causes musical sounds when a tube of glass or 

 metal, or even of paper, is held over it. Such an arrangement is 

 known a* the hydrogen harmonicon, but any combustible gas will 

 produce a similar effect. 



The equivalent of hydrogen is 1, and its combining volume 2. Its 

 combinations with other elements or radicals are called hydridet or 

 hydraretf, 



Hydrogen combines with oxygen in three different proportions, 

 forming, 



1. Protoxide HO water. 



2. Binoxide HO, oxygenated water. 



S. Teroxide HO, ozone. 



1. Protoxide of Hydrogen, or Water (HO) will be treated of in a 

 special article. [WATER.] 



2. Binoxide of Hydrogen (HO,). To prepare this compound, twelve 

 parts of binoxide of barium, obtained by passing oxygen gas over 

 baryta heated to low redness, are dissolved in two hundred parts of 

 water containing as much hydrochloric acid as will saturate about 

 fifteen parts of baryta. Solution having been effected by gentle 

 stirring, the whole of the baryta is then precipitated by a slight excess 

 of sulphuric acid, added drop by drop. Another twelve parts of binoxide 

 of barium are now added, and the precipitation of the baryta effected 

 as before. This process is continued until about one hundred parts of 

 binoxide of barium are consumed, care being taken to keep the mixture 

 well cooled, and to filter it after every other addition of the binoxide. 

 A tolerably strong solution of binoxide of hydrogen is thus obtained, 

 containing, however, much hydrochloric acid. The latter is removed 

 by the addition of sulphate of silver, and the sulphuric acid thus intro- 

 duced got rid of by carbonate of baryta. Finally, the solution is 

 placed in vacuo over sulphuric acid for a few days, when the water 

 evaporates and leaves the binoxide of hydrogen. The latter Ixidy 

 also volatilises in vacuo, but far less quickly than water. 



Binoxide of hydrogen thus prepared must be kept in long glass 

 tubes, closed with stoppers, and surrounded with ice. Notwithstanding 

 these precautions, however, it slowly decomposes into water and free 

 oxygen gas. It is a colourless, transparent liquid, of sp. gr. 1'452. It 

 is unaltered by a temperature 54 degrees below the freezing point of 

 water. It has a harsh, bitter taste, bleaches litmns paper without 

 reddening it, and when placed on the hand whitens the cuticle and pro- 

 duce* violent itching. Heat rapidly decomposes it. Contact with most 

 metallic oxides not only causes violent separation of oxygen, but at the 

 same Aimo the oxides themselves are reduced to the metallic state. 

 Binoxide of hydrogen appears to combine with some of the hydrated 



acids, as it is far less decomposable in their presence than when 

 alone. 



Oxygenated water is a term that has been applied to binoxide of 

 hydrogen, but is now usually restricted to the solution formed by 

 saturating water with oxygen gas. 



3. Teroxide of Hydrogen (H0 3 ). The gases that are evolved when 

 water is decomposed by a current of electricity are well known to 

 possess a peculiar odour. The body that communicates this property 

 has for some years been called ozone (from ofa, " I smell ") ; but it is 

 only recently that M. Baumert has proved it to be the teroxide of 

 hydrogen. The presence of hydrogen in this remarkable compound 

 M. Baumert demonstrated by passing the gases (oxygen and ozone) 

 evolved from the positive pole of a water-decomposing apparatus 

 through a long drying tube containing pumice-stone moistened with 

 sulphuric acid, and then through a tube the inner surface of which 

 was coated with anhydrous phosphoric acid, and one portion of which 

 was gently heated ; water was thus produced, ;md made evident by the 

 solution of the film of phosphoric acid on that part of the tube through 

 which the gas was making its exit, while the film on the opposite part 

 was quite unaltered. 



Teroxide of hydrogen decomposes iodide of potassium, the excess of 

 oxygen it contains over and above that necessary to form water with 

 its hydrogen liberating its equivalent of iodine from the iodide of 

 potassium, just as chlorine or bromine does, Taking advantage of this 

 fact, M. Baumert ascertained the composition of ozone, prepared as 

 above, by passing the gas for several hours through a weighed bulb 

 apparatus containing iodide of potassium solution, with an arrange- 

 ment for preventing loss of water by evaporation. The increase in 

 weight after that time gave the quantity of ozone that had passed into 

 the apparatus ; an estimation of the iodate of potash formed, showed 

 how much oxygen, exclusive of the elements of water, was contained 

 in that weight of ozone, while the difference between the weight of the 

 oxygen and the total increase in weight of the apparatus, gave the 

 weight of water that had been formed from the decomposition of the 

 ozone. The mean of three such experiments proved that the ozone in 

 question was teroxide of hydrogen, thus : 



II 

 SO 



HO, 



By calculation. 

 4 



. . 90 



100 



By experiment. 



4-1 

 95 



100-0 



Other Compoundi of J/ydrog<!H. With sulphur, selenium, iodine, 

 bromine, chlorine, fluorine, and tellurium, hydrogen forms combina- 

 tions called hydracidt. With nitrogen, it forms the powerful salifiable 

 base ammonia; and with phosphorus, arsenic, antimony, and potassium, 

 it forms the several hydrides. A description of each of these com- 

 pounds will be found under the name of the element with which the 

 hydrogen is united. 



HYDROKINONE. [Krxojiic GROUP.] 



HYDROLEIC ACID. [Oi.mc ACID.] 



HYDROMARGARIC ACID. [MAKOAUIC ACID.] 



HYDROMARGARITIC ACID. [MAROABIC ACID.] 



HYDKOMKLLON. [MELLOX.l 



HYDROMELLONIC ACID. [MELLONIC ACID.] 



HYDRO'METER (KSup, water, and nfrpov, a measure) is an instru- 

 ment for determining the relative densities or specific gravities of 

 fluids. The principle of the hydrometer is this : It is known that 

 when a body is immersed in a fluid, it loses as much of its weight as is 

 equal to the weight of that portion of the fluid which it displaces. 

 [HYDROSTATICS.] Thus, if a body suspended from the extremity of 

 one arm of a balance be counterpoised by weights applied to the other 

 arm, and while thus suspended it be immersed in a vessel of water, it 

 will be found that one arm of the balance will preponderate, and that, 

 in order to restore the equilibrium, as much weight must be applied to 

 that arm from which the'body is suspended as is equal to th weight 

 of the water displaced. Hence, if the same body be immersed succes- 

 sively in two different fluids, the portions of weight which it will 

 thereby lose will be directly proportional to the specific gravities of those 

 fluids ; because the diminution of weight is always equal to the weight 

 of the fluid displaced, that is, to the magnitude of the body multiplied 

 into the specific gravity of the fluid. The above supposes the body to 

 be specifically heavier than the fluid. If it be lighter, it will float upon 

 the surface, so that its tendency to descend, or iti weight, will then be 

 entirely counteracted by the fluid ; from which it appears that, when 

 a body floats upon the surface of a fluid, the weight of the portion of 

 fluid displaced is equal to the entire weight of the body. Now, since 

 the weight of the fluid displaced by a floating body is constant (l>cing 

 always equal to the weight of the body), whatever may be the density 

 of that fluid, it is obvious that if we can determine how much of the 

 body is immersed, we may immediately deduce the specific gravity of 

 the fluid ; because, when the weight is constant, the specific gravity 

 varies inversely as the bulk. 



Upon this principle is constructed the instrument known by the 

 name of Syken't* hydrometer, which is that employed in the collection of 

 the spirit revenue of Great Britain. It consists of a thin brass stem 

 about six inches in length, passing through and soldered to a hollow 

 ball of the same material, and about one inch and a half in diameter. 



