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saltpetre and Norwegian saltpetre. It is used as a manure and for 

 making other nitrates and derivatives of nitric acid. Nitrolim or 

 calcium cyanamide is another calcium compound containing nitro- 

 gen of atmospheric origin. When lime is heated with coke or 

 charcoal, both the elements of the lime unite with the carbon. 

 The oxygen forms a gaseous substance, the calcium a solid com- 

 pound known as calcium carbide. This substance is familiar to 

 most of us, as its use in preparing acetylene gas is well known. 

 Besides its use for this purpose it is employed in making the 

 nitrolim to which I referred just now. Atmospheric nitrogen is 

 passed over the calcium carbide at a very high temperature, and 

 nitrolim results. Its chief use is as manure. Under the influence 

 of moisture and carbonic acid it undergoes a complex decomposi- 

 tion in which, no doubt, bacteria play an important part. Various 

 intermediate substances are formed, and finally the nitrogen is 

 brought into a form suitable for use by plants. 



Another calcium compound valuable for manurial purposes is 

 that known as superphosphate of lime. It is made by acting with 

 sulphuric acid on bone-ash or on one of the various minerals which, 

 like bone-ash } consist mainly of calcium phosphate. Over 

 700,000 tons are manufactured annually in Great Britain. Bone- 

 ash and the mineral phosphates just mentioned are the source of 

 the phosphorus used in making matches. It is the presence of 

 that element that gives them their chief value, still, as they are 

 calcium compounds I thought it not unfair to mention them. 



We have not, however, by any means exhausted the inventory 

 of the uses of lime itself. It has, for instance, an important part 

 to play in the sugar industry. Milk of lime, i.e., the milky-looking 

 liquid obtained by stirring together slaked lime and water, is added 

 to the expressed juice of the sugar cane to neutralise the acids 

 present and to aid in the removal of certain other impurities which, 

 if allowed to remain, would lower the quality of the sugar. In the 

 case of beet-root sugar, the use of lime is not less essential. The 

 solution obtained by steeping the pulped beets in water or by some 

 alternative method, is treated with milk of lime to get rid of acids 

 and salts. The excess of lime is removed by a current of carbonic 

 acid gas, and the juice, freed from many of its original impurities, 

 is often subjected to a repetition of the treatment, but this time at 

 the boiling point, to complete the removal of the objectionable 

 constituents. 



There is no obvious connection between the lump of sugar 

 which a man adds to his breakfast coffee and the boots which, 

 when breakfast is over, he puts on to go to his office or for his 

 morning walk, yet a link may be found between them in lime. 

 Before hides or skins can be tanned they must be cleaned and 

 prepared, hair or wool must be removed, and so on. Lime water 

 or milk of lime is used for these purposes. The hides are steeped 

 in lime pits until the hair can easily be removed by scraping. 

 The lime having thus played its part must not be allowed to remain 

 on or in the hide. The removal is brought about by soaking in 



