38 



On the Induration of Mortar. 



as I have found from experiment, would rapidly deposit crystallized 

 carbonate of lime and assist the mortar in hardening. The deposit 

 takes place even under water, shewing, perhaps, a property necessary 

 in water cements. 



In Spain, and in some parts of this country, a mixture of chunam and 

 fish oil is used for the purpose of defending the bottom of vessels, to 

 save the expense of coppering them. This composition gets soon 

 covered with sea-shells, and it is necessary to chip it 01T and replace it 

 every now and then. When first applied, it is soft as putty, but in the 

 course of a fortnight it hardens, and after some time becomes so hard 

 that it is cut with a heavy axe with great difficulty. It appears likely 

 tf*%jt this would be found a very useful water cement, especially with 

 sea water, and, as it is not likely to make any great difference with 

 what description of oil it is made, a cheap one, too. 



I am not chemist enough to answer the question whether the sugar 

 and the oil act upon lime after being changed into a state analogous to 

 oxalic acid. It may be useful to remark that the three substances are 

 composed of the same elements, and not in very different quantities, 

 and that oxalic acid is that which has the strongest affinity for lime as 

 well as for magnesia. 



The quantity of lime that should be mixed with sand, in order to 

 produce the strongest mortar, has been frequently discussed, and very 

 various indeed have the results of these discussions proved — as, 

 indeed, might have been expected from experiments which do not ap- 

 pear to have been carried on in the same manner. The fir&>t paragraph 

 of these remarks shews a good and easy method of trying the cohesion 

 experimentally. Theoretically, it may be considered that all that is 

 not brick or stone in a building must be mortar, in order that it should 

 be one solid mass. In like manner, it may be considered that all that 

 is not sand in a quantity of mixed mortar which has dried should be 

 crabonate of lime. Now, if you take a tumbler, and fill it with dry 

 sand, you may afterwards pour into it without spilling rather more than 

 half as much water (by measure) as you put sand : consequently the 

 sand does not fill half the space that it occupies. Hence it would 

 appear that mortar should consist by measure of equal quantities of 

 carbonate of lime and of sand — or further, that, since 630 parts of car- 

 bonate of lime contain 356 of lime, that the proportion should be 356 

 parts: of lime (or 468 parts of hydrated, or slaked, lime) to 630 parts of 

 sand — which is nearly in the proportion of two to three. It is to be re- 

 marked that if coarse sand be mixed with fine a larger part of the space 

 occupied will be filled; and also, that this proportion of two to three 

 is that in use among maistries in this country. 



With regard to the quantity of mortar that should be used with bricks, 

 this must depend on the closeness and goodness of the work. If 1,000 



