The first of the above tables requires no explanation. In the second the quantities of oxygen which 100 parts of each species of wood absorbs from the air, in effecting its complete combustion, have been calculated. These represent the relative values of the woods as fuel, since the quantities of heat developed by combustion are proportional to these quantities of oxygen.

It will probably excite, at first, some surprise that the different sorts of wood do not follow the order, which their price or their value in common life seems to assign them.

The proportion of carbon contained by them will be found pretty nearly equal, but the chief difference is in that of the oxygen. When therefore, we consider that 100 parts by weight of hydrogen, require for combustion 800 parts of oxygen, while 100 of carbon demand but 262 of oxygen, it will be easy to understand why the wood of the linden tree, which contains a large portion of hydrogen, should develope more heat by its combustion,

than that of the beech, which contains but a small proportion of the same ingredient.

It follows, likewise, from this view, that the value assigned to the woods in common life, is quite independent of their absolute combustible value, and must be determined by other considerations. For the domestic purposes of heating apparatus, as in kitchen fire-places, stoves, &c., a fuel is required which is less remarkable for giving an intense, than a moderate, durable, heat; consequently those species of wood will be preferred which abound least in hydrogen, and have a higher proportion of carbon. The linden, the firs, and the pines, are rich in hydrogen. This it is, chiefly, which, united with a certain proportion of carbon, yields the gas that constitutes the flame of a wood fire. These kinds of wood yield a quick and an intense heat, with a brisk flame, leaving a light and scanty charcoal. On the quantity of hydrogen in wood depends that of the charcoal remaining after combustion, for the hydrogen forms with the carbon, carburetted hydrogen gas, and necessarily takes up some of the carbon. With beech, on the contrary, it produces a short flame, proportionally much less vivid, and it is to the remaining coals, which continue to glow for a long time, that so high a value is attached. Oak, both with regard to these properties, and to its actual value, holds a middle rank between these two species of wood,

If we could construct our fire-places according to the exigencies of each kind of wood, the value of each kind for the purposes of life, would be exactly expressed by its place in the second table. But this is not the case. The following example shows how this value is equalized. Throughout the north the chief fuel employed is the wood of fir and pine. In those countries, however, it is not burnt in cast-iron stoves, but in those of clay or masonry, by which the quick and intense heat is absorbed and retained by the stoves, which give it out but slowly. Here then the heating apparatus is constructed according to the fuel, and to attain the same end fir and pine will be preferred, weight for weight, to beech wood.

In regard to the quantity of charcoal which the carbonization of each species of wood will yield, it must be inversely proportional to the quantity of its hydrogen; for the more hydrogen there is, the more carbon will it take up in forming carburetted hydrogen gas, and the less carbon will there be left. Results in practice, on a large scale, are entirely in accordance with this view of the subject. What has already been said applies to woods taken in equal weights. But wood is generally bought and sold by measure, and consequently a difference in price arises from the difference of specific gravity in the different kinds.

According to the experiments of Mr. Bull, in the United States, a cord of dry wood contains in pounds, the following quantities, viz:

* In France, wood has for several years been sold by weight.

Yellow pine,

Jersey pine,
Pitch pine,
White pine,

It follows, that under an equal volume of hickory, oak, or beech, there is far more matter capable of generating heat, than in the case of poplar or of any of the pines.

Soft and light wood offers to the oxygen a larger surface, since it burns more readily and perfectly than the harder and more compact varieties. The latter only undergo a process of distillation from the interior parts, and when the included gases have been burnt, there remains a residuum of carbon from nineteen to twenty-five times greater than in the case of the lighter woods.

The experiments of Peclet have demonstrated clearly that the radiant heat of ignited gases, that is of flame, is infinitely weaker than that of red hot coal. Hence it results that the proportion of radiant heat must be very different in burning the different kinds of wood. The harder and more compact any species of wood is, and the less it contains of hydrogen, the greater is the quantity of radiant heat it is capable of producing. The soft woods give the least quantity of radiant heat. We ought then to reject the soft woods containing much hydrogen, from all those processes of heating which particularly require radiant heat. To heat boilers where the radiant heat is to be applied directly to the surface heated, in open fireplaces and stoves, the hard woods are to be preferred. But when the object is to produce a high temperature at a certain distance from the fire, as in stoves and furnaces of masonry, in the manufacture of porcelain and glass, the wood which produces the most charcoal has the least value, for the furnace is choked up with coals, without producing the effect of a flame which extends on every side, and applies directly, by contact, to the surface to be heated.*

Manufacture of Sulphate of Soda. A new process for obtaining this salt has been secured by patent to Richard Phillips, Lecturer on Chemistry at St. Thomas' Hospital, and which he thus describes:

It is well known that when certain kinds of the persulphuret or bisulphuret of iron, commonly called iron pyrites, or martial pyrites, and sometimes merely pyrites, are exposed to the action of the air and of moisture, the sulphur which the pyrites contains is, for the most part, by oxidizement, converted into sulphuric acid, and the iron which the pyrites contains is also, by oxidizement, converted into oxide of iron, and the sulphuric acid and oxide of iron thus formed, combining, they constitute with water a solution of sulphate of iron, copperas, green copperas, or green vitriol, with an excess of sulphuric acid, and the heaps of pyrites which are thus exposed to air and moisture for the purpose of preparing sulphate of iron, or green vitriol, are called copperas, or pyrites, beds. The liquor which is yielded by the action of the air and moisture upon the pyrites of these copperas beds, is an aqueous solution of sulphate of iron or green vitriol, with excess of

The use of pine and other soft woods is, however, preferable in steam boilers, where a great extent of fire surface is intended to be exposed to the contact of flame. TR.

See Annales de Chimie et de Phys. for July, 1835, for a valuable paper by M. Berthier, entitled, Examen de quelques combustibles.

sulphuric acid, and this liquor I call "the entire liquor," meaning thereby that it contains the whole, or nearly the whole, of the sulphuric acid formed by the action of the air, and of moisture, on the sulphur of the pyrites in the copperas beds, as above described.

The use of this entire liquor (on account of the large quantity of sulphuric acid which it contains) is one of my said improvements in the process of manufacturing sulphate of soda. For this purpose I take sixty parts (by weight) of common salt; frequently called muriate of soda, and sometimes chloride of sodium, and put it into a reverberatory furnace of the usual construction, and I add to it such a quantity of the entire liquor before described as would, if mixed with a sufficient quantity of an aqueous solution of acetate, nitrate, or other convenient salt of lead, give a precipitate of sulphate of lead which would weigh, after proper washing and drying, about one hundred and sixty parts, these one hundred and sixty parts of sulphate of lead, indicating the presence of sulphuric acid equal to about fifty parts, by weight, of concentrated liquid sulphuric acid, or oil of vitrol, and which are required for the decomposition of sixty parts of common sait, so as to convert it into sulphate of soda. I also take the specific gravity of the entire liquor, and on future occasions when its specific gravity is the same, or nearly so, I determine the quantity of it to be used with sixty parts of common salt, by its specific gravity alone, and without repeating the trial as to the quantity of sulphate of lead which is yielded by a given portion of it. And I may here observe that the greater the specific gravity of the liquor, the greater will be the advantage to the manufacturer.

The entire liquor, and common salt, being well mixed in the reverberatory furnace, I heat the mixture, as usually practised in the decomposition of common salt by sulphuric acid, occasionally stirring it, until acid vapours cease to arise from it; the residue of this operation is a mixture of oxide, or peroxide, of iron and sulphate of soda, and usually a small but unimportant quantity of common salt; I heat this residue in water to, or nearly to, its boiling point, in any convenient vessel, and when the water is nearly or sufficiently saturated, I suffer the peroxide of iron to subside, and the clear solution being conveyed to proper vessels, it yields, by cooling, crystals of sulphate of soda.

Having now described what I consider to be the best process for obtaining sulphate of soda by decomposing common salt with the entire liquor, I will proceed to describe another of my said improvements, which consists in the use, when circumstances render it eligible or convenient, of the crystalized sulphate of iron, green copperas, or green vitriol, obtained from the entire liquor (or in any other mode) by the usual processes.

For this purpose I reduce about one hundred and fifty parts, by weight, of the crystallized sulphate of iron, or green vitriol, to powder, and mix it with sixty parts, by weight, of common salt, and I heat the mixture in a reverberatory furnace in the same manner as before described, and I treat the residue in the same way as already described with reference to the residue obtained when the entire liquor is used.

Another of my said improvements consists in the use of the solution remaining after the separation of the crystals of sulphate of iron in the ordinary process of making green vitriol, and which solution is termed the "mother waters;" the strength of this solution, and the quantity of it to be used with a given weight of common salt, I determine by means of the proportion of sulphate of lead which it yields, exactly in the same manner as described with respect to the use of the entire liquor; I also take its specific

gravity for the reason already stated with respect to the entire liquor, and treat the mixture and residue as already mentioned with regard to those processes previously described.

Rep. Pat. Inv.

Means of facilitating the expression of oil from seeds. A patent was taken in March, 1835, by Henry Walker Wood, of London, for applying a diluted acid, (muriatic acid for preference) previously to pressure, whereby the seed, it is alleged, will part more thoroughly with the oil. The following is the method he prescribes-"Take about one hundred pounds of seed, and, during the time that it is being ground, sprinkle it regularly with about three pounds two ounces of muriatic acid, diluted with about six pounds and a quarter of water; this is supposing the acid to be of 1160 specific gravity. By the process of grinding and sprinkling, the diluted acid will be intimately mixed with the ground seed. This mixture of seed, acid and water, is to be permitted to stand for some hours, twelve will be generally found sufficient, though the time will vary, depending on the quality of the seeds, but this will be soon ascertained by practice, and a short time longer or shorter will not materially influence the result of the process. The mixture is next to be submitted to pressure by placing it in bags, and disposing the same in the press, in the following manner; first, a bag of seed, next a plate of iron, then a bag of seed, and so on. I prefer an hydraulic press, and the pressure is to be exerted in the usual manner. By this improvement it will be found that the seed will part with the oil more thoroughly, and a larger quantity of oil will be obtained from a given quantity of seed than heretofore. Having now described the invention, and the manner of performing the same, I would remark, that although I have stated exact quantities of acid and water to be applied to a certain quantity of seed, yet I do not confine myself thereto, as it will be found that the quality of the seed will in some degree vary the quantities of the diluted acid, which will produce the best effect, but this must in a great measure depend on the judgment of the workman, which can only be obtained by practice, but the above quantities are given as average quantities; nor do I confine myself to the use of the particular acid named, or to the applying the diluted acid precisely at that part of the operation called grinding, as the same may be mixed subsequently but before the pressure is applied.

Ibid.

Hancock's Steam Carriage. One or two of this gentleman's steam carriages have been travelling without intermission since the 11th of May last. That steam locomotion on common roads is both practicable and safe to the passengers and the public, he has proved; it now remains for him to show (which it will be seen by the following letter, containing a statement of his late performances, he promises shortly to do,) that his travelling has been economical, so as to return a fair profit to any capitalist who may embark his money in a speculation of the kind.

Mr. Hancock is now the only engineer with a steam carriage on any road. Sir Charles Dance, Colonel Maceroni, Dr. Church, Messrs. Ogle, Summers, Squire, Russel, Redmond, Heaton, Maudsley, Frazer, and a host of others-where are they? Echo answers-"Where!" Strange to say, however, we see steam carriage companies advertised, whose engineers