108 



THE POPULAE EDUCATOR. 



13. Quelle chanson chantiez-vous ce matin ? 14. Je chantais une 

 chanson italienne. 15. Avez-vous eu peur de me parler ? 16. Je n'ai 

 jamais eu peur de vous parler. 17. Avez-vous apporW mon livre? 18. 

 Je ne 1'ai pas apporte\ 



EXERCISE 103 (Vol. I., page 394). 



1. Why did you not write more quickly this morning ? 2. Because 

 I was afraid of making mistakes. 3. Were you not afraid of offending 

 that lady ? 4. I feared to offend her, but I could not do otherwise. 

 5. What were you painting this morning ? 6. I was painting an his- 

 torical picture. 7. What was your dyer dyeing ? 8. He was dyeing 

 cloth, silk, and linen. 9. What colour was he dyeing them ? 10. He 

 was dyeing the cloth black, and the silk and linen green. 11. Were 

 you conducting the young Pole to school, when I met you ? 12. I was 

 conducting my eldest son to church. 13. What were you reading ? 



14. I was reading hooks %vhich I had just bought. 15. Did you not 

 know that that gentleman is dead ? 16. I had forgotten it. 17. How 

 much was the watch which you broke worth ? 18. It was worth at 

 least two hundred francs. 19. Was it not better to remain here than 

 to go hunting ? 20. It was much better to go to school. 21. What 

 was yottr friend saying to you? 22. He was telling me that his 

 brother is back from Spain. 23. Did you not (use to) go hunting 

 every day when you were living in the country ? 24. I often went 

 fishing, 25. My brother went to school every day when he was here. 



LESSONS IN CHEMISTRY. XVIII. 



CLASS I. METALS OP THE ALKALIES. 



POTASSIUM. 



SYMBOL, K ATOMIC WEIGHT, 39'1 SPECIFIC GRAVITY, 0'865 MELTING 

 POINT, 62-5. 



SIB HUMPHRY DAVY, in 1807, included this metal in the list 

 of brilliant discoveries which he made by means of the electro- 

 lytic action of the galvanic current. He slightly moistened 

 Some hydrate of potash, in order to render it a conductor, and 

 then applied it to the poles of a strong battery. At the nega- 

 tive wire the metal potassium appeared. 



The preparation of the metal may be conducted with much 

 less expense by either of the following processes : 



1. Melted potassic hydrate is allowed to run over iron turn- 

 ings in a bent gun-barrel, which is raised to a considerable 

 temperature in a charcoal furnace. The iron deprives the 

 potash of its oxygen, and the metal potassium passes over in 

 vapour, which is condensed in naphtha. 



2. The present mode of procuring the metal, however, was 

 invented by Curandau. It consists in intimately mixing G9 

 parts of potassic carbonate and 12 parts of carbon. This 

 mixture is heated in a crucible, and then the porous mass is 

 broken into small pieces and introduced into an iron retort, 

 which is submitted to a high heat. 



KjOCO,+ 2C = SCO + 2K 



explains the action and intimates that the mixture is entirely 

 converted into carbonic oxide and potassium. The delivery tube 

 from the retort projects a few inches out of the furnace, and 

 dips into a receiver of naphtha, which is kept cool by being sur- 

 rounded by water. 



Properties. At ordinary temperatures potassium is a soft 

 metal. When cut, it is found to be of a white colour. It has 

 great affinity for oxygen, and will at a red-heat deprive almost 

 any gas of that element. As we have seen, it can even decom- 

 pose water, the heat evolved in the action being sufficient to set 

 fire to the escaping hydrogen, the flame of which is tinged by 

 the beautiful purple colour which is characteristic of the " potash 

 flame." 



Potash is the widely-diffused oxide of potassium. It takes 

 its name from the fact that it is obtained from the " ashes " of 

 the wood with which the "pot" has been boiled. Plants have 

 the power of abstracting potash from the soil. It is a con- 

 stituent of granite rocks, from which all soils are originally 

 derived. The wood-ashes when washed have their potash dis- 

 solved by the water, and upon evaporating this solution "Pearl- 

 ash" is obtained, which is really not potash, but an impure 

 carbonate of potash, and forms one of the sources from which 

 our potassium and its salts are derived. 



Potassic Hydrate, or " Caustic Potash " (HKO). If thin slices 

 of potassium be exposed to dry oxygen, Potassium Monoxide 

 (K 2 0) is formed a white, brittle substance. It absorbs moisture 

 with avidity, forming potassic hydrate (HKO), in which it will 

 be seen that one atom of K has been replaced by one of H. 



The usual method of obtaining this compound is by boiling 

 one part of potassium carbonate with twelve parts of water, 

 and adding slaked lime made from two-third parts of quick- 

 lime. The reaction is 



K a OCO.,+ H 3 OCaO = 2 (HKO) -f CaOCO,. 



The calcium carbonate (chalk) sinks to the bottom, while the 

 clear liquid is decanted and evaporated without contact with the 

 air. The residue may be cast into sticks, but the fusion should 

 be carried on in silver vessels. 



It deserves the name " caustic " from its severe action oa 

 animal tissues. 



Potassium Carbonate (K 2 OCO 2 ). This is imported from the 

 forests of Eussia and America in large quantities as pot-ashes or 

 pearl-ashes. 



To render it pure it is calcined like potassio hydrate. It is 

 a strong alkali, and if exposed long enough to the air, absorbs 

 moisture and becomes an oily liquid. By passing a current of 

 carbonic dioxide through a solution of this salt, one of the 

 atoms of K may be replaced by one of H, forming hydric potas- 

 sium carbonate -^ | OC0 2 . This salt is not so soluble as the 



carbonate, and is almost neutral, having no effect on reddened 

 litmus paper. 



Potassium Nitrate, Nitre, or Saltpetre (KN0 3 ) is found as an 

 efflorescence upon the soil in certain districts in the East Indies. 

 The soil favourable to its production is of a loose limy nature, 

 mixed with decomposing felspar, which contains potash, and of 

 necessity there must be present more or less organic matter. 

 The process by which the salt is produced is called " nitrifica- 

 tion," and is little understood. It is supposed that the decom- 

 posing organic matter which contains nitrogen gives off ammonia ; 

 that this ammonia becomes oxidised into nitric acid, which with 

 the potash forms nitre. In Sweden, the farmers have " nitre 

 plantations," that is, they throw all the refuse of their farms, etc., 

 into a heap, which they continually turn to expose it to the air. 

 After three years, the bed is lixiviated, or washed with water. 

 To this water pearl-ash is added, by which the nitrates of lime 

 and magnesia are decomposed, and the nitrate of potash formed. 

 Upon evaporation the nitre crystallises out, the insoluble car- 

 bonates having fallen. 



Saltpetre contains nearly one-half its weight of oxygen, with 

 which it readily parts when in contact with carbon. To this 

 property it owes its commercial value, it being the chief ingre- 

 dient of 



Gunpowder, a compound which is said to have been discovered 

 about 1336 by a certain Cordelier monk of Breslau, named 

 Berthold Schwartz. This is unlikely, for the Arabians and 

 Chinese had used an explosive substance for many centuries, 

 and even Eoger Bacon, who died about 1294, in his treatise 

 " De Nullitato Magiss," gives a receipt for making a kind of 

 gunpowder. Our English powder consists of 75 parts of nitre, 15 

 of charcoal, and 10 of sulphur. The process of manufacture 

 carried on at the Government mills at Waltham Abbey is the 

 following : 



The ingredients are with great care procured perfectly pure. 

 The charcoal is that of alder-wood ; the proper proportion of 

 each to make a "charge" of 52 Ibs. is taken and ground 

 separately into impalpable powder. The powders are then 

 mixed, and water is added to make them into a paste ; this is 

 placed beneath two broad wheels fixed on the same axle, one of 

 which rolls within the other, on a smooth iron plate. By this 

 " incorporating mill " the ingredients are thoroughly mixed, and 

 the paste is then submitted to a pressure of 70 tons on the 

 square inch; the "press cake" thus produced rings, when struck, 

 like a piece of metal. This cake is next broken by spiked 

 rollers, and the grains sifted on sheets of parchment, perforated 

 with different sized holes ; these being placed one above the other, 

 the large grains are delivered into their proper receptacle from 

 the top sieve, the finest grains being found on the lowest. The 

 powder in this condition is of a dull leaden colour, and is glazed 

 by being placed in a barrel which revolves very rapidly on its 

 axis ; the grains polish each other by mutual friction ; occasion- 

 ally a little black-lead is added. This latter process renders 

 the powder less liable to contract damp. 



When ignited the following reaction occurs : 

 2KNO 3 + 3C + S = K a S + 3CO a + 2N ; 

 that is, the solid becomes entirely gae, with the exception of the 



