The yield of charcoal is from 17 to 20 per cent. when made in the ordinary way, but by the use of super-heated steam to regulate the temperature, and maintaining it at 300°, the yield may be increased to 33 per cent. The proportion of carbon in the product, however, is diminished, being only about 65 per cent., while the oxygen, hydrogen, and nitrogen are correspondingly increased. By increasing the temperature to 400° the yield is decreased to 20 per cent., and the carbon in the product increased to 80 per cent. At 1000° the yield is 18.7 per cent., and the carbon in the product 82 per cent. A larger yield is obtained when the process is carried out slowly and when the wood is dry. The most esteemed charcoal for pharmaceutical purposes is prepared from willow twigs two or three years old. It is official as Carbo Ligni, U. S. P.

The best charcoal is hard and brittle, breaking with a lustrous fracture and emitting a metallic sound when struck. As ordinarily prepared it is a poor conductor of heat and electricity, but when prepared at a high temperature it is more compact and becomes a better conductor. Like all other varieties of carbon, it is infusible. Wood charcoal possesses in a marked degree the power to absorb and condense gases. One volume of boxwood charcoal was found by Hunter to absorb the following volumes of gases under ordinary pressure and at a temperature of o° :

On account of this property charcoal becomes valuable for absorbing noxious gases and destroying them. It also possesses the power of decolorizing dark liquids, although not in the same degree as the next variety.

(d) Animal charcoal is prepared by charring bones and other animal matter. The variety known as bone-black is formed when bones are heated in closed iron retorts; the by-product in this case is "Dippel's animal oil." Animal charcoal is official in two forms, Carbo Animalis, U. S. P., and Carbo Animalis Purificatus, U. S. P. The crude article is in dull-black, granular fragments or powder; it is odorless and tasteless and insoluble in water or alcohol. When ignited it should leave about 86 per cent. of a white ash, consisting of calcium phosphate and

carbonate, which should be completely soluble in hydrochloric acid with the aid of heat. The purified animal charcoal is prepared by digesting in a water-bath for twenty-four hours two parts of the crude preparation with three parts of hydrochloric acid and fifteen parts of water, washing, drying, and heating to dull redness.

When purified, animal charcoal is a dull-black powder, odorless, tasteless, insoluble in water and all other solvents. When ignited at a high temperature, with a little mercuric oxide and free access of air, it should leave only a trace of residue. Purified animal charcoal possesses the power of absorbing coloring matter from solution. It will withdraw the color from solutions of indigo or logwood, and remove the fusel oil from alcohol. It absorbs alkaloids and astringent compounds from their solutions, and gives them up to boiling alcohol. Many of the domestic filters for the purification of water are constructed of animal charcoal and sand. Perhaps the most extensive application of animal charcoal is in the decolorizing of sugar, and in the purification of the heavy portions of petroleum, by which such preparations as petrolatum are made.

(e) Lampblack. This variety of carbon is in very fine powder. It is obtained from the smoky flame of many bodies rich in carbon, as resins, when their combustion takes place without much access of air, and the products are condensed. This condensation is accomplished by passing the products through a series of chambers. Rosin and petroleum are most frequently employed in the preparation of lampblack, but the product is not pure. The purification is effected by heating for some time in a current of chlorine. A very pure lampblack is made from the natural gas of Western Pennsylvania and Ohio. The product from this last source is very pure and is sometimes known under the name of diamond black. Lampblack, when pure, is a velvety black, impalpable powder, having a specific gravity of 1.729 at 17°. It should mix readily with water, and yield no color to alcohol and ether when agitated with them, showing the absence of oily impurities. It is used to give a black color to paints and inks, not only on account of its intense black color, but also because of its indestructibility.

COAL.

Coal is classified as a variety of carbon, although it contains, besides that element, considerable quantities of oxygen, hydrogen, nitrogen, mineral matter, and frequently sulphur.

Our present supply is the product from the decomposition of plants of a former age, this decomposition having taken place under great pressures without access of air, and in the presence of moisture.

Owing to the differences under which their formation took place, we have several different varieties of coal. They may, however, be arranged into two classes, Anthracite and Bituminous coals.

Anthracite is found in this country most abundantly in Pennsylvania, and in lesser amount in Rhode Island. An inferior variety is found in Wales, France, Saxony, and Southern Russia. It contains about 90 per cent. of carbon and only very small quantities of sulphur. It is hard, with a conchoidal fracture and an iron-black color, frequently displaying iridescence. It burns with but little flame and gives out an intense heat. The volatile matter is contained in it in small amount, being from 6 to 7 per cent.

Bituminous coal is found in all parts of the world. It is much softer than anthracite, and contains a larger proportion of volatile matter. It is used extensively in producing coke and in the manufacture of illuminating gas, in which process it yields many useful by-products.

Cannel coal is a variety of this class which, on account of its large proportion of volatile matter, is much used in England for gas making. The carbon of bituminous coal varies from 70 to 91 per cent., the sulphur from 0.40 to 2.25 per cent., the nitrogen from 1.00 to 2.50 per cent., and the ash from 0.75 to 20 per

cent.

Lignite is a brown coal of more recent formation than the two preceding varieties. It frequently retains the structure of the wood from which it was formed.

Jet is a variety of this brown coal, so compact as to take a fine polish.

CARBON AND HYDROGEN.

These two elements unite directly with each other, although with some difficulty and always under peculiar conditions. The number of such compounds, mostly formed by indirect means, however, is very great. These compounds of carbon and hydrogen, when associated with oxygen and nitrogen, become wellnigh innumerable, and make up the material of Organic Chem istry.

The subject of organic chemistry, therefore, is confined to the

t

consideration of the compounds of carbon and their derivatives, and the classification of these is based on several series of hydrocarbons, or compounds of carbon and hydrogen.

It will be sufficient at this point to give some description of two or three compounds of these two elements in order to have them for comparison with the hydrogen compounds of the preceding elements.

Marsh gas is the first member of the paraffin series of hydrocarbons. It occurs free in nature wherever vegetable matter is undergoing decomposition in the presence of moisture. This is always noticeable where leaves and other vegetable matter are under water, and the bubbles which rise when such a mass is disturbed are composed chiefly of this gas. It also occurs in coal seams, giving rise to the fire damp of the miners, and is the explosive element in mine disasters. The very lightest part of petroleum consists largely of this gas, and escapes as soon as the oil is relieved of its pressure on coming to the surface. Closely associated with this is the natural gas, which has marsh gas for its chief constituent. Natural gas is found in great abundance in Pennsylvania, Ohio, West Virginia, and Indiana. In all these places it has been successfully used for heating, and, after treatment, also for lighting. It has been found especially valuable in metallurgical operations. The supply, which at first seemed inexhaustible, has in the past few years perceptibly diminished, and it is only a question of some years more, in many localities, when a return will be made to other fuels.

Preparation.-Marsh gas may be prepared by heating sodium acetate and hydrate in an iron or copper retort, when the following reaction takes place :

In practice it is preferable to substitute calcium oxide for a part of the sodium hydrate, thereby preventing the mixture from liquefying. This is best accomplished by using sodium acetate, I part, and soda-lime, 4 parts. Soda-lime is made by slaking calcium oxide with a solution of sodium hydrate of such strength that 2 parts of calcium oxide shall be mixed with 1 part of

sodium hydrate. The mixture is then dried and heated in an iron or Hessian crucible, after which it is preserved in a tightlyclosed bottle.

Marsh gas may be obtained absolutely pure by adding zinc methyl to water:

Another method of preparation consists in passing a mixture of carbon disulphide vapor and hydrogen sulphide over red-hot metallic copper :

2H2S + CS2 + 8Cu =

4Cu2S + CH4.

This process is of interest because of the fact that every one of the compounds employed is strictly inorganic and may be made directly from elementary matter, thus rendering it possible to prepare many of what are considered organic compounds synthetically.

Properties.-Marsh gas is colorless, odorless, and tasteless, and is insoluble in water. At a pressure of 54.9 atmospheres and a temperature of -81.8° the gas liquefies. This liquid commences to boil at -164° under ordinary atmospheric pressure. Marsh gas is combustible, and when mixed with 2 volumes of oxygen or 10 volumes of air it explodes with considerable violence. By the electric spark the gas is slowly decomposed into its constituent elements. When a mixture of I volume of marsh gas and 2 volumes of chlorine is exposed to direct sunlight or the flame of a taper, a sudden reaction takes place, with the formation of hydrochloric acid, and the separation of carbon as a black, very finely divided powder. Marsh gas is not considered poisonous, since when mixed with air to the extent of 9 per cent. it has been inhaled by workmen in coal mines without serious inconvenience.

This gas is the first member of the second series of hydrocarbons, known as the olefine series, to which it has given the

name.

Preparation.-The gas is best prepared by heating, in a capacious glass flask, a mixture of 1 part of alcohol with 6 parts of