July 25, 1889] 



NATURE 



309 



gunpowder (see Fig. 3). A small boy then scrambles down the 

 hole, and easily excavates the soft cova a little under the congelo, 

 forming an opening called the taza, or cup. The taza only 

 is then filled with a slow-burning gunpowder, made of nitrate of 

 soda on the premises, a tamping put into the tiro, and the charge 

 exploded. The valuable caliche bed is thus simply lifted and 

 partially broken, without being blown into dust ; and a party of 

 men separate the nitrate from the worthless beds, and carry it to 

 the factory, or maquina. 



Caliche varies so much in composition that it is almost im- 

 possible to give a typical analysis. One very rich specimen gave : — 



Per cent. 

 Nitrate of soda... ... ... ... 50 



Chloride of sodium ... ... ... 26 



Sulphate of soda... ... ... ... 6 



,, magnesia ... ... ... 3 



Insolubles ... ... ... ... 15 



but a more average sample might be taken to contain one-third 

 nitrate ; one-third salt ; and one-third earth. 



The problem for the manufacturer is to get the nitrate without 

 the salt and earth ; and the simple basis of the whole process 

 rests on the fact that, while salt is rather more soluble in cold 



Feet. 



— 6 



— 5 



— 4. 



Java. 



Taza. 



-3 



-2 



— I 



-0 



Fig. 3. 



than in hot water, nitrate of soda is about four tim.es more soluble 

 in hot than cold water. It is also evident that, if a salty rock is 

 washed with water already saturated with salt, no more of that 

 material can be absorbed. The raw caliche is therefore first 

 crushed into small pieces, washed with six changes of hot water, 

 by what is known as the " passing system " similar to that used 

 for lixiviating soda ash. After the last washing the waste caliche 

 is known as rtpio (refuse), and is thrown on to a rubbish heap ; 

 while the strongest hot water, which is drawn off the caliche, 

 is known as caldo, or " broth. " 



The hot broth then runs for twenty minutes into a settling 

 tank, where earth and salt are deposited, and after that into 

 great square shallow bateas, or troughs. In about five days 

 the greater part of the nitrate has been deposited nearly pure at 

 the bottom of the batea, and a yellow orange liquid, known as 

 aqua vieja, remains on the top. This liquid is drawn off, the 

 nitrate crystals drained, thrown on to a flat floor or cancha, to dry 

 for three weeks, and then when bagged are ready for the market. 



In many factories the atjua vieja is then pumped into the iodine 

 room. 



One sample of this fluid gave the following analysis : — 



Per cent. 



Nitrate of soda 28 



Sulphate ,, ... ... ... ... 3 



Chloride of sodium ... ... ... 11 



lodate ,, ... ... ... 22 



Sulphate of magnesia ... ... ... 3 



Water 33 



100 



besides a; mall quantity of iodide of sodium, which cannot be 

 utilized. 



To separate the iodine a mixture of nitrate of soda and coal 

 dust is formed into a pyramid and set alight, by which means a 

 crude carbonate of soda is formed. Fumes of burning sulphur 

 are then drawn through a solution of this carbonate, and an acid 

 solution of sulphite of soda is produced. A suitable quantity of 

 this last liquid is added to the aqua vieja, when iodine is preci- 

 pitated in an impure form, which after sublimation becomes the 

 iodine of commerce. 



Nitrate of soda thus manufactured contains from 95 to 96 per 

 cent, of pure nitrate, with less than i^ per cent, of salt, the 

 remainder being chiefly water. The nitrate is sold in Liverpool 

 for about \os. a hundredweight, while the iodine is disposed of in 

 London for about yl. an ounce. 



It is impossible to examine a bed of crude nitrate of soda, 

 without thinking how it got there. We have described the facts- 

 as to the position of some beds relative to the lie of the country, 

 and also explained the character of the layers which adjoin the 

 caliche, but unfortunately we can do little more. Numerous 

 theories have of course been started, but none have either 

 accounted for all the facts, or obtained general acceptance. 

 This may perhaps be the case because no competent geologist 

 has as yet thoroughly examined the nitrate beds in different 

 parts of the country, but still a few remarks on the subject may 

 be desirable. There is no doubt that the coast range and the 

 Pampa have been elevated out of the sea at a comparatively 

 recent period, but it is also equally certain that since that elevation 

 the climate was at one time far more rainy than at present. Alt 

 over the plains there are dry river-beds, and the flanks of the hills 

 are scored by water-cut channels which could not have been 

 carved out under the existing conditions of rainfall. This would 

 make it doubtful whether the nitrate could have been deposited 

 immediately after upheaval. 



It may be noted as a curious fact that the stones found both in 

 the costra, caliche, and congelo are usually angular ; but in one 

 nitrate ground I have certainly seen rounded pebbles in all these 

 formations. 



Much difficulty is always found in accounting for the existence 

 of nitric acid. The existence in some deposits of a layer of guano 

 under the caliche is a very suggestive fact, but unfortunately our 

 knowledge of the circumstances is far too limited to allow of any 

 generalizations on the subject. The presence of iodine in caliche 

 has often been appealed to as pointing to the decomposition of 

 beds of seaweed ; but it may be remarked that there is a good 

 deal of iodine about in the neighbouring mountains in the form 

 of iodide of silver. We can only repeat the statement that the 

 origin of nitrate of soda is at present unknown. 



Whatever may have been the origin of the beds, there is no 

 doubt that their existence is due to the rainlessness of the west 

 coast of South America, so that a few remarks on the climate 

 and weather of the caliche districts may be of interest. All along 

 the coast we find three belts of climate and weather : that of 

 the coast, that of the Pampa, and that of the Sierra. 



Iquique may be taken as a typical station on the coast, and 

 here fortunately a considerable amount of material has been 

 accumulated through the labours of the Meteorological Com- 

 mission for Chili. Speaking broadly, temperature at any season 

 will rarely exceed 8o°-85°, or fall below 50° at any hour in the 

 coldest season ; and as the air is always tolerably dry the climate 

 is very bearable and wholesome. The wind blows from south to- 

 south-west throughout the year during the day, but at night 

 sometimes comes more off the land from some point of east. 

 Though nothing approaching to a gale ever blows at Iquique,. 

 the effect of distant storms is often experienced in the form of a 

 heavy surf, which entirely stops any shipment of nitrate. The 

 surf days, or Bravesas as they are called, occur most irregu- 

 larly, for while in some years only nine days are recorded, other 

 seasons have been credited with no less than forty-three days of 

 enforced idleness. Contrary to the usual opinion, three or four 

 slight but real showers fall every year, mostly in the months of 

 June, July, and August, though this precipitation does not extend 

 inland to the Pampa. The .sky is usually clear, but a low stratus 

 or strato-cumulus cloud often covers the sea and coast range 

 during the forenoon, but dissipates as the sun gains power. 



On the Pampa, where all the nitrate ojicinas are built, the 

 temperature may rise to 85° or 90° on the hottest days ; and at 

 night may fall to the freezing-point during the winter months. 

 The air is much drier than on the coast ; and though rain has been 

 known to fall, it is certainly of very rare occurrence. Cloud is 

 more rare on the Pampa than on the coast ; but nearly every 

 night a very thick wet fog settles over the plain. This is locally 

 known as camanchaca, probably an Aymara word, whose 



