color. When clays are to be used for making pressed brick for fronts or ornamental purposes, it is best to avoid all clays containing epsom salts or sulphate of magnesia.

The following may be a guide to finding the magnesia in clays:

Take some clay; dry the clay by heat; reduce it to a fine powder, andsaturate with sulphuric acid. Then dry and calcine the mass at a red heat, in order to convert any sulphate of iron (copperas) that may be present to a red oxide; it is then dissolved in water and sulphuret of lime is added, to separate any remaining portion of iron; then pour off the liquid and evaporate it, and the crystals that form, if any, are the sulphate of magnesia. This should be done by a chemist.

Sulphuret of Lime is made of two parts lime, ten parts water. in testing the clay.

one part flower sulphur,
This is the mixture used

Of course, if the sulphate of magnesia is found, the clay is not fit for front or ornamental brick.

Yet it is possible to wash some clays and carry off the magnesia.

Another method of analyzing clay is as follows:

Grind the clay to a powder, and add diluted muriatic acid until it ceases to effervesce; heat it until the liquid evaporates, the residue being a thin paste; then add water and shake it; then filter the mixture and dry what is on the filtering paper by heating-this gives the insoluble matter; if magnesia is contained add clean water so long as any precipitate is formed; quickly gather the precipitate, and wash with pure water. The residue from washing is the magnesia.

Sand. Whatever variety of sand is used in making mortars or cements, it should be granular, hard and gritty, sharp and angular, with a polished surface, and nearly uniform in size.

Sand, when perfectly fit to be used in mortar, will bear the test of being rubbed between the hands without soiling them.

Sand is not increased in volume by moisture, nor contracted by heat.

1

The finest sand screened should pass through a wire mesh one-thirty-second of an inch square; the medium size, onesixteenth of an inch mesh.

The quality of mortar or cement depends chiefly upon the quality of the sand. The common practice of using unclean sands, or road drifts, argillaceous loams, and even alluvium or common soil cannot be too speedily abolished. Masons are apt to compound the mortar with the soil used from the foundations regardless of quality, suitability or the natural consequences of its employment.

Clean, sharp bank sand, free from loam and screened, is generally used in mortars for buildings.

As calcium or lime is used more extensively for mortars than anything else, it may be very desirable to give the various compounds.

CHAPTER VII.

On the preparation of Common Mortar. -The lime, when perfectly burnt in the kiln, should be packed in casks or airtight vessels, and kept free from all moisture, and should be opened only as required.

Unslacked dry lime fresh from the kiln is termed caustic or quick-lime. After water is added to it, it is called slacked lime. The exact quantity of water for slacking is in proportion to the quality of lime; the fat or rich will absorb more than the poor or lean. No definite rule can be given for all localities for the use of water. The average is twice the weight of water to the lime, but this is only an approximation. It is important that the mortar should be used fresh.

The best or richest limes are made from pure carbonates of lime, which usually increase to twice their volume when slacked, but do not harden well in damp places. Poor limes do not expand much in volume; neither do poor limes harden well in damp places.

Limes that have been ground are usually of inferior quality, often mixed with refuse lumps and air-slacked lime. Mortar, stuccoes or cements prepared from ill-burnt lime continue soft and dusty for a long time after being made whereas well-burnt and slacked limes soon become thoroughly indurated.

Rich limes hiss, bubble and throw off great heat during the process of slacking.

The purest limes require the largest proportion of sand and water, and harden in less time than the common limes.

Various substances are sometimes added to mortar to increase the tenacity, and they impart thereto the principles of hydraulic cement to a greater or less degree.

They chiefly consist of burnt clay, ashes, scoriæ, iron scales and filings, broken pottery, bricks, tiles, etc. They are useful in mixing with lime or mortar to increase their hardness, but they must be pure and reduced to a fine powder.

Some of the mason builders in New York and vicinity, who are large contractors, make building mortar for brick walls of the following proportions :

One barrel of lime,

Six barrels of sand-sharp bank sand,

which is calculated to lay one thousand bricks.

The average number of bricks laid on buildings around New York, Brooklyn, etc., for each man is one thousand per day. For mortars for this purpose many kinds of limes are used-Thomaston, of Maine; Briggs, North River; Snowflake lime, of Pleasantville, N. Y., etc., etc.

The proportion of one measure of quick-lime, either in lumps or ground (when lumps exceed three inches each way they require to be broken), and five measures of sand, is about the average used for common mortar by many masons. However, architects generally specify one part of lime to three of sand.

Mortar generally increases in volume one-eighth more than the bulk of loose sand.

In walls that are exposed to dampness, no lime should be used, as it will never harden properly. Cement should be used, or use burnt clay or fine brickdust, and mix it with the lime, as this forms a kind of hydraulic cement.

Shell lime is about the same as that from the purest lime-stone.

The average weight of common hardened mortar is from 105 to 115 pounds per cubic foot.

Common grout is merely common mortar made so thin as to flow like cream. It is used to fill the interstices left in the mortar joints of masonry or brickwork, and is perhaps best when a little cement is added.

Mortar should be applied wetter in hot than cold weather, especially in brickwork, otherwise the water is too much absorbed by the brick. To prevent this, dip each brick for an instant in water in some kind of vessel, especially if dusty, as it impairs the adhesion.

Where there is a heavy working strain brought on piers, or parts of walls, it would be best to use some proportion of cement, as the tenacity or cohesion in some mortars is not to be relied upon until four to six months after being used. This is only important where structures are heavily loaded or of considerable height.

The tenacity of good mortar is usually fifteen and onehalf pounds per square inch, or one ton per square foot.

The crushing load may be taken at fifty tons per square foot.

Laying bricks or building walls when the mortar freezes always produces weak walls, and brings expense afterwards.

Common mortar of ashes is prepared by mixing two parts of fresh slacked lime with three parts of wood ashes together, and when cold to be well beaten, in which state it is usually kept for some time; and will resist alternate moisture and dryness. By some it is considered equal to some of the water cements.

A kind of cement plaster used around exterior foundation walls is made of one-quarter Portland cement, threequarters lime, and two parts sand, with water sufficient to make a mortar. But Rosendale cement, small proportion of lime, if any, and one part sand to one of cement is the best; and even with this, where it is exposed to dampness, it is best to coat the cement with a coat of asphaltum.

To Color Mortars. This may be done by the use of various colored sands. There are yellow, silver and grey sand to be had in many localities. Colored mica, put on the surface of stucco work with a thin mixture of limewater and lime, first wetting the surface, leaves a durable and sparkling finish. Pulverized bricks, yellow or red, may be used. Pulverised dust from colored marble, also basalt dust, are all durable. Ochres seldom stand exposure to the weather.

Where black has been used for pointing the joints of brickwork, the mortar requires so much black to make the color that the mortar becomes poor, and washes off.

Spanish brown is a species of earth of a reddish brown color, which depends upon the sesque-oxide of iron.