A composition of a similar nature, is the blue mortar, commonly used in London, for setting the coping of buildings and other works much exposed to the weather. It is made with coal cinders and lime, but is seldom prepared with the requisite attention.
Ash-mortar is used in some parts of England, and is prepared by slacking two bushels of fresh meagre lime, and mixing it with three bushels of wood ashes; this mass is to lie till it is cold, and then to be well beaten ; in this state it is kept for a considerable time without injury, and even with advantage, provided it lie thoroughly beaten twice or thrice over before it is used. This cement is superior to terras mortar, in situations alternately exposed to wet and dry ; hut under water, terras mortar has the advantage.
The scales which are detached by the hammering of red hot iron, have been long known as an excellent material in water-works. Mr. Smeaton appears to have been the first person who tried the relative strength of mortar made of the oxide of iron, and several other compositions. The scales being pulverized and sifted, and incorporated with lime, are found to produce a cement equally powerful with puzzolana mortar, when employed in the same quantity. N r. Smeaton having been successful in his experiments on these materials, was induced to try others of a similar nature. Having substituted roasted iron ore for the scales, he found that this also gave to mortar the property of hardening under water, though it required to be used in greater proportions than either puzzolana or terras. Two bushels of argillaceous lime, two of iron ore, and one of sand, being carefully mixed, produce 3.22 cubic feet cement, fully equal to terms mortar. If the common white lime be employed, it would he advisable to use equal quantities of all the three ingredients.
With respect to the water used in the preparation of aquatic cement, that of rivers or ponds, where it can be procured, is to be preferred to spring water : but for works exposed to the action of the sea, it is usually more convenient, and equally advantageous in other respects, to use salt water.
The Lorica mortar is a composition which at one time had obtained considerable celebrity in France, and was employed in many large works. It was invented, about seventy years ago, by M. Loriot, who imagined that he had discovered the process used by the Romans. The principle of the invention eonsiAted in adding to any quantity of mortar, made in the usual way with lime and sand, but prepared rather thinner than usual, a certain portion of iplick-lime in powder. The
lime-powder being well incorporated with the mortar, the mass 'heated, and in a few minutes acquired a consistence equal to the best plaster-of Paris ; at the end of two days it became as dry as an ordinary cement at the end of several months ; and when the ingredients w ere well proportioned, it set without any cracking. The quantity of powder varied from to of the other materials, according to the quality of the lime : too much. horning and drying up the mass ; and with too little, its peculiar advantages being lost. The pro portions are essential, but can only be determined by actual experiment.
Loriot's process was at one time. as we have observed, very, much in vogue, but has now fallen into disuse. Founded on the fike conception that the induration of mortars was the mere result of a more or less rapid desiccation, and presuming it to be possible to obtain this end by the intro duction of a powerful absorbent, it met with the usual fate of error, and sunk into disrepute.
Mr. Smeaton says of this composition—" I have made trial of this method, both in small and in large ; for however little likelihood of advantage a proposition may contain, yet, when this concerns a physical process, nothing can be safely concluded but from actual trial ; and I must candidly own that the effect was much better than I had expected ; for I found the composition not only set more readily than mortar as eonunonly made up, but muoh less lialde to crack, and consequently, if this cement was made use of in water-build ing, it was less apt to re-dissolve, because it would more speedily get set to a firmer consistence, and so as more ably to resist the water from entering its pores ; but when the water was brought upon it, in whatever state of hardness it was at the time, it at best remained in that state without any further induration, while the water remained upon it ; and, as I expect, would so remain, till it had some opportunity of acquiring hardness by further drying." Indeed, thr the purpose of quick concretion, various materials are recommended to be added, such as brick and tile powder, and forge scales. The following is an approved receipt : one measure of bricks, finely pounded ; two mea sures of fine river-sand ; old slacked lime in sufficient quan tity to make a mortar in the usual manner. and sufficiently liquid to quench the lime-powder, which is added to the same quantity as that of*the pulverized bricks.