EBPOET OF CHEMICAL LABORATORY 



221 



considerable, sand and clayey matter. The Department of Works experienced considerable 

 difficnlty in employing the lime made from this material, especially in interiors where the 

 plaster was found to blister and peel. Mr. F. Blurphy, of the same Department, called my 

 attention to the exceptionally poor ciuality of the mortar used in the construction of certain 

 buildings. In places, I was told, the mortar could not only be scraped away with the 

 greatest ease, but once the outer covering was removed, the interior was found to run away 

 almost as readily as loose sand. Samples of lime from several sources, used for this purpose, 

 were sent to the laboratories for examination. One of these was only tested qualitatively. 

 It was found to contain no lime at all — evidently a mistake in the sampling. Two other 

 samples gave the following results : — 



Marks Pasquali Lolos 



True Lime (a O) 58-.3 ... o4 7 



Sand, Clay, etc 28-1 ... 31-8 



Undet 13G ... 13-.') 



Cause of bad 

 quality of lime 



Total 100-0 1000 



There was nothing in these figures to account for the unsatisfactory results obtained. 

 Ultimately the explanation was found in the method of working. As already mentioned, the 

 limestone near Khartoum is of very irregular quality and contains a considerable amount of 

 foreign stone. As it is not easy, by mere inspection, to detect this useless material in the 

 burnt lime, nor to estimate the amount present, it has been the practice of contractors to 

 purchase the lime only after it has been slaked and the worthless material sifted out. 

 There would be little objection to this method provided the lime were used at once ; but, as 

 a matter of fact, it was delivered, or used, in many cases, days and even weeks after slaking. 

 With lime of like composition such a practice is fatal. In the presence of so large an 

 amount of clay, the lime " sets" to a certain extent, like a cement, and the best results can 

 only be liad by using as (juickly as possible after slaking. Of course, where the lime has 

 been allowed to stand, slakeil, and in dry powder, for weeks, not only is the eifect of the 

 hydraulic character of the lime lost, but absorption of carbon dioxide from the air takes 

 place to such an extent that the lime becomes practically worthless. These points were 

 quickly grasped by Mr. Murphy ami the energetic measures taken to insure the use onlv of 

 freshly-slaked lime were followed, we are informed, by satisfactory results. 



The ideal method of employing lime of this hydraulic character is that which, as I am 

 informed by Mr. Dupuis, obtains in India. The lime is derived from a so-called " kankery " 

 formation, consisting of nodules and root-like masses containing, in addition to calcium 

 carbonate, a considerable proportion of clay and sand. This is burnt with wood in rather 

 shallow kilns. After cooling the entire mass is ground, and the powder so obtained furnishes 

 an excellent hydraulic lime. In use, water is only added at the time the admixture with 

 sand or other material, is made. The maximum hydraulic effect is secured in this way. ■' Kanker' 



Foreseeing the need for lime for building purposes throughout the Sudan, a number of 

 samples of limestone were collected by Mr. Dupuis, Inspector General of the Sudan 

 Irrigation Service. Some of these are "kankery" formations, similar to those of India, and 

 there is every reason to believe that excellent results would bo had by treating the lime 

 produced from them either in the ordinary way, or, if hydraulic lime is required, by the 

 Indian method detailed above. Others are more nearly pure limestone and would furnish a 



