efforts to improve the dwellings of the poorer classes, has invented one arrangement of hollow bricks in which there is the requisite "bond," without the use of "headers," (or bricks which pass through the full thickness,) so that there is less chance for the wet to get through; and in thin walls of cottages, this invention must be highly commended. The more common mode of getting rid of the damp is by coating the wall with cement. This is certainly effectual, but it is the source of great expense, becomes the excuse for much bad brickwork, and is the occasion of want of attention to architectural design, and has to do with most of such inferiority as exists in general taste. If the walls were built of not less than one brick and a half length in thickness, with the work properly executed, all objects could be answered. It is not uncommon on the inside of walls, to contrive a hollow space by means of timbers called quarters, and lath and plaster; but in such cases as we have referred to, it would be better to keep the damp from getting into the wall.

14. Walls which are otherwise well built, may still be subject to long-continued damp. If the bricks have been laid during very wet weather, the house may remain damp for a surprising length of time. We have known cases where brickwork laid in the autumn, has not been dry before the end of the summer in the next year. And where sand in the slightest degree impregnated with saline matter, like that from the sea-shore, has been used for mortar, or plaster, the walls will be always in a damp state. Where the ground of the foundation is not well-drained, damp even rises up the porous material of the wall. To prevent this, a layer of asphalte, or someother impermeable contrivance, is sometimes placed in the bed of one of the lower courses of brickwork, over the whole area of the walling.-There should be some vacant space below the lowest floor of the house, and this space should be well ventilated by iron "airbricks" in the external walls. Some old houses where there is no cellar story are found very defective in this particular. Before taking such a house it would be well to notice whether the floors get dry soon after being

washed, and also in what state are the carpets and matting, and the wall-papers near to the skirting. A cellar story, even with the space under the floor, may be damp from the wetness of earth against the outer walls. Such contact may be easily prevented by placing a thin wall outside the main wall, so as to leave a narrow vacant space all round the house. The causes of damp sometimes elude detection for years, and perhaps are at last traced to a spring under the house, or to the leakage of a pipe, or some other matter whereabout neglect had taken place in the original building. Entire houses may be found uninhabitable from causes never to be discovered. These details, however, are such as would require very lengthened description.

15. The great requisite in taking a house-more especially a new one, where the character of the builder is not known-is to be alive to the fact of the really momentous nature of the task. We have noted some points in regard to which inquiry may be made, and others will suggest themselves. The house should be visited at different states of the weather, and appearances, such as we have referred to, should be looked for. The situation of the drains, and the fact of their perfect delivery of the contents from off the premises, should be known. Any offensive smell, not readily and permanently removed by pouring down a few quarts of water, should be conclusive testimony to the unhealthiness of the place. A small quantity of water in the "trap" of a drain, is required to prevent the return of effluvia, and this water, when a house has been unoccupied, may have dried up.

Many persons have dated an inroad into their constitution, permanent, though not discovered for a long interval, to a change in a place of residence. A wellconstructed house, with all its defensive parts and its working machinery in order, is really a great emanation from human skill, and an humble imitation of the work of the Great Architect of the human form,-acquaintance with the anatomy of which has indeed been held as an essential element of knowledge for the practical designer and constructor.-E. HALL.

THE BUILDERS.

ALL are architects of Fate,
Working in these walls of Time;
Some with massive deeds and great,
Some with ornaments of rhyme.
Nothing useless is, or low,

Each thing in its place is best;
And what seems but idle show,
Strengthens and supports the rest.
For the structure that we raise,
Time is with materials filled;
Our to-days and yesterdays

Are the blocks with which we build.

Truly shape and fashion these,

Leave no yawning gaps between ; Think not, because no man sees, Such things will remain unseen.

In the elder days of art,

Builders wrought with greatest care Each minute and unseen part,

For the gods are everywhere.

Let us do our work as well,

Both the unseen and the seen;
Make the house where gods may dwell
Beautiful, entire, and clean.

Else our lives are incomplete,
Standing in these walls of time;
Broken stairways, where the feet
Stumble as they seek to climb.
Build to-day, then, strong and sure,
With a firm and ample base;
And ascending and secure
Shall to-morrow find its place.
Thus alone can we attain

To those turrets, where the eye
Sees the world as one vast plain,
And one boundless reach of sky.

LONGFELLOW.

Chemistry.

BY EDWARD FRANKLAND.

LESSON I.

NON-METALLIC ELEMENTARY BODIES.

1. THE non-metallic elementary bodies, or metalloids, are thirteen in number, and are named as follows:

:

2. The metalloids are distinguished from the metals, chiefly by their being non-conductors of heat and electricity, and by their not possessing the metallic lustre. It has, however, been already mentioned, that the three metals-arsenic, antimony, and tellurium— are intimately associated with the metalloids in their chemical relations, although in their physical properties these elements are indubitably metals; we shall therefore study them in connection with the metalloids. Thus associated with arsenic, antimony, and tellurium, the metalloids may be grouped into the following five divisions; the separate members belonging to each being characterized by a certain community of chemical character.

1st Division.-Oxygen, Sulphur, Selenium, Tellurium. 2nd Division.-Hydrogen.

3rd Division.-Nitrogen, Phosphorus, Arsenic, Antimony.

4th Division.-Chlorine, Bromine, Iodine, Fluorine. 5th Division.-Carbon, Boron, Silicon.

3. Althought his grouping is of service, in indicating the more or less close chemical resemblance of the several bodies contained in each division; yet it will be necessary, in studying the separate elements, to depart occasionally from this order of classification, and to give priority to those elements, which possess the highest importance, either from the interest attached to their

compounds, or from the extensive range of their affinities.

4. OXYGEN. This element is a colourless and invisible gas, constituting rather more than one-fifth of the bulk of the air we breathe, and forming a large part of nearly all the materials composing our globe. Eight out of every nine tons of the water of oceans, seas, rivers, and lakes, are oxygen, and fully one-third of the total weight of the solid crust of our globe is due to the same element. Oxygen is essentially necessary for the processes of respiration and ordinary combustion, and neither animal nor vegetable life can be supported, without a due supply of this gas in an uncombined state. The affinities of oxygen are so extensive and powerful that most of the other elements exist naturally in combination with it; so that the free oxygen present in the atmosphere, nearly represents that portion which has remained in excess, after the saturation of the other constituents of matter; and to this portion, thus remaining in excess, the fitness of our globe for the existence of plants and animals is in great part due.

5. Although oxygen is such an abundant constituent of matter; yet, owing to its intense affinities, it can be procured in a pure state, only from a comparatively small number of its compounds. It cannot be obtained directly from the atmosphere; because we are acquainted with no substance which is capable of removing the other constituent of air-nitrogen, with which the oxygen is mixed; but, by causing the atmospheric oxygen to combine with some substance from which it can again be easily expelled, it is not difficult to obtain, thus indirectly, oxygen from the air in a state of purity. For instance, if we expose metallic mercury to a current of air, at a temperature little short of its boiling point, it gradually absorbs oxygen, and becomes converted into peroxide of mercury; a substance which is well adapted for the preparation of oxygen in a pure state.

6. To procure oxygen gas from peroxide of mercury, a quantity of this compound should be placed in a retort (fig. 1), to the neck of which a bent tube is connected, for conveying the gas to a vessel in which it can be