Name of Class.

Percentage of Clay, associated with Carbonate of Lime only, or with

Carbonate of Lime and Carbonate of

Magnesia.

Behaviour in slaking after being wetted.

Behaviour in setting under Water.

Feebly-Hydraulic

5 to 12 p. c.

Pauses a few minutes, then slakes with decrepitation, development of heat, cracking, and ebullition of vapour.

Firm in 15 to 20 days. In 12 months as hard as soap - dissolves with great difficulty, and in frequently renewed water.

Ordinarily Hydraulic

15 to 20 p. c.

Shows no sign of slaking for an hour, or perhaps several hours - finally cracks all over, with slight fumes, development of heat, but no decrepitation.

Eesists the pressure of the finger in 6 or 8 days, and in 12 months as hard as soft stone.

Eminently Hydraulic

20 to 30 p. c.

Very difficult to slake - commences after long and uncertain periods - very slight development of heat, sensible only to touch - very often no cracking, or powder produced.

Firm in 20 hours - hard in 2 to 4 days - very hard in a month - in 6 months can be worked like a hard limestone, and has a similar fracture.

Varieties Of Lime In Common Use

Fat Limes. - White chalk, marble, the Oolitic limestones, and shells, when calcined, furnish the fat limes in ordinary use. A great variety of fat limes is found in England, Scotland, and Ireland.

Oysters and other shells require burning at a high temperature. They contain gelatine, which is converted into charcoal, and burns with difficulty; the result is a tendency to produce a badly slaking lime.

Hydraulic Limes

Grey Chalk Lime (called "stone lime" in London) is of a feebly hydraulic character.

It is obtained from the lower chalk beds in the South of England, the present supplies coming from Hailing, Dorking, Lewes, Petersfield, Mers-tham, etc.

This lime is usually of a light buff colour, and slakes very freely. "When used with two parts of sand in brickwork, a good sample should sensibly resist the finger-nail at a month old.

Lias Lime varies greatly in its properties according to the locality of the beds from which it is procured, some being only moderately hydraulic, and others eminently so.

The raw stone is of a dark blue colour (hence the lime is called "blue lias "), and the burnt lime a pale grey.

It slakes very sluggishly, and should set well in wet situations (according to its composition) in from one or two to several days.

This lime is sold both in lump and ground. The latter is, as a rule, the best, as the softer stones, containing more clay, are selected for grinding, but it may be adulterated with sand, or be air-slaked (see p. 202).

The lime is ground to nearly the same fineness as Portland cement (see p. 162), and sold in sacks, or, for export, in casks.

Mr. Reid says that limestones which approach nearest to the analysis given in the Table, p. 150, "should have the preference."

Lia8 lime is procured chiefly from the Midland and South-western counties - the best known being that from Barrow-on-Soar, in Leicestershire; from Watchet, in Somersetshire; Lyme Regis, in Dorset; Whitby, in Yorkshire; and Rugby, in Warwickshire.

The Carboniferous Limestones yield very valuable hydraulic limes, among which may be mentioned the Halkin Mountain limestone, from Holywell, in Flintshire; the Aberthaw lime, found near Cardiff; lime found near Berwick, in Northumberland, etc.

The Arden lime, found in this formation near Glasgow, is of an eminently hydraulic character,, and has been much used for docks and other important work. It partakes rather of the character of a Roman cement, and will not stand a large proportion of sand.

The Milton or Hurlett lime, and the Kilbride lime, from the same neighbourhood, are of a similar description.

Hydraulic lime is found also in Fifeshire, at Dunbar, etc. etc.

The Magnesian Limestones, found in Durham, Yorkshire, Derbyshire, Don-caster, and Notts (see p. 57), also furnish hydraulic limes, which are sometimes of a powerful character.

In Ireland the calp limestone yields a hydraulic lime, but it is very variable in quality.1 A good hydraulic lime is obtained from the Gillogue quarry in the carboniferous formation near Limerick.

The lias has not been met with to any extent in Ireland, and is usually imported.

Artificial Hydraulic Lime may be made by moderately calcining an intimate mixture of fat lime with as much clay as will give the mixture a composition like that of a good natural hydraulic limestone, of which the product should be a successful imitation.

A soft material like chalk may be ground and mixed with the clay in the raw state. Compact limestone, on the other hand. is more commonly burnt and slaked in the first instance (as being the most economical way of reducing it to powder), then mixed with the clay and burnt a second time.

1 Wilkinson's Practical Geology of Ireland.

Lime so treated is called "twice kilned" lime.

The mixture may be made by violently agitating the materials together in water by machinery, or by grinding them together in a dry state, afterwards adding water to form them into a paste.

The paste in either case is moulded into bricks, which are dried, calcined, and otherwise treated like ordinary lime.

Artificial hydraulic limes are not much manufactured or used in this country.