inches deep; and in this place the pots, or the plants without pots. The distance apart of plants in the bed should always be such as to admit the leaves to spread their full extent, without the plants touching each other when full grown. Or if it be thought that tan bark contributes either to the health, size, or flavour of the pines, this may be placed over the floor of slates of a due depth, instead of earth, and the pots plunged into it.

The space under the slate floor may be profitably appropriated to the growth of mushrooms, asparagus, sea kale, &c.

263

ESSAY

ON THE

NATURE AND APPLICATION OF STEAM.

IT has long since been demonstrated, that steam is infinitely superior to every other medium for dif fusing an equal degree of heat through any given space. Fire applied by one furnace or boiler to circulate steam through a range of metallic pipes, chambers, or boxes, will communicate a more equal degree of heat, to the extent of a mile or further, than it could be made to do 500 times repeated by any other means. The number of accidents which have occurred from imperfect construction, bad arrangement, and carelessness, have impressed most people who have heard of steam engines, with ideas of danger in the appropriation of steam for any purpose; but the improvements made in the construction and arrangement of an apparatus by Mr. Hague, and for which he has obtained a patent, must convince every person who will give it consideration, that there is less

danger attending this than any of the usual modes of applying steam or fire; and particularly in heating rooms and houses, and in boiling liquids.

Every operation required in a dwelling-house or manufactory to be effected by heat, may, by adopting this plan, be conducted by one fire, and which may be placed without, or detached from, the house or buildings. So that not only all annoyance from smoke, sulphureous vapours, ashes, &c. is avoided, but the danger from fire is materially lessened, and the hazard in insuring reduced.

It is well known, that by far the greater number and the most afflicting accidents, which have occurred from the use of steam, have been occasioned by boiling or evaporating the boiler dry, and, whilst hot, throwing in cold water, which, by producing a sudden contraction of the metal, or expansion of the water, has either fractured or burst it.

The peculiar value of Hague's apparatus, here recommended, consists in its returning the condensed steam back into the boiler immediately, and in proportion as the condensation takes place, without exposure to the atmosphere, or its being detained in any intervening vessel, and without requiring any additional force or labour: consequently, the boiler never can, by any accident or negligence, be evaporated dry; and, unless any steam be intentionally or carelessly wasted, the quantity of water at first put in, must remain undiminished for any length of time.

In this arrangement, the steam boiler need only be placed a few inches lower than the under part of the pipes, chambers, pans, boxes, or vessels to be heated, and all air being excluded from such pipes, &c., and all the water produced by condensation being returned into the boiler as fast as it takes place, the whole surface or expanse is kept clear for the full action of the steam, and the heat is thus constantly and regularly kept up and sustained without variation or partial ebullition; and the effect of this is, that water in any quantity may be kept boiling with the utmost equality, and a proportionate degree of heat kept up in any length of pipe or extent of chamber, box, or vessel, that may be required, with a pressure of steam below 6lb. per inch; but, if required, this principle and arrangement may be applied so as to be worked with the same facility and safety, under any degree of pressure however high. Another important advantage resulting from returning the condensed steam into the boiler as it takes place, is a very great saving of fuel; for the water that is carried off, by being converted into steam, being as rapidly returned, as, by giving out its heat, it is again converted into water, its temperature cannot be reduced more than a few degrees: consequently much less fuel will be required to convert it into steam again, than must be necessary when the steam is blown off and wasted, and its loss supplied with cold water. The temperature of the water returning from steam condensed in working a still

charged with water, at a pressure of 6lb. per inch, is proved to be 211 degrees Fahrenheit.

The method of applying this principle to the boiling of liquids, is by attaching a double or hollow bottom to the pan or boiler, so constructed as to form a sufficient chamber or receptacle for the steam to expand over, and come in contact with, the full surface of the bottom. By these means, the action of heat is exerted on every part exactly at the same time, and precisely equal in degree. It is well known that heat, when in action, always ascends, and, consequently, a very slight comparison will clearly show the superiority of this arrangement over every other that has hitherto been adopted in the process of boiling; whether for the purpose of making decoctions, extracts, and solutions, as in brewing, dying, colour-making, &c., or for the purpose of evaporating and concentrating, as in the operations of drying, distillation, and crystallization, or for liquefaction, as in purifying oil, melting resin, tallow, &c.; for, by the common mode of applying heat, it is almost impossible to prevent the fire from drawing to one part of the boiler or pan more than another, and when this is the case, to bring the whole contents of a vessel to an uniform heat, that portion of the liquid immediately above, or in contact with the fire, is necessarily raised to a much greater degree of heat than would be required if the heat were equally diffused through the whole,