38 



THE POPULAR EDUCATOR. 



root, augur, and pearla of a fine quality. These islands are 

 claimed by the French Government as a dependency of France, 

 a settlement having been effected at Tahiti in 1843. The 

 island of Tahiti, it should be said, consists of two peninsulas, 

 each consisting chiefly of a lofty central mountain, and con- 

 nected by a narrow isthmus. The population of the group is 

 estimated at 9,000. 



The Marquesas Islands were occupied by the French at 

 about the same time that they made a settlement in Tahiti. 

 The largest of the group is Noukahiva, which has a superficial 

 extent of about 200 square miles only ; the area of the whole 

 cluster being estimated at 12,000. The islands are productive, 

 yielding every kind of tropical vegetable and fruit ; but the 

 inhabitants, unlike the majority of the men of Micronesia and 

 Polynesia, are fierce and intractable, and given to cannibalism : 

 indeed, the presence of the French settlers, and the exertions 

 of the missionaries, have failed in inducing that progress in 

 civilisation that contact with European nations and the intro- 

 duction of Christianity have effected in the Sandwich Islands. 



The Austral or Southern Islands are so called from their 

 position with regard to the Society Islands. The Low Archi- 

 pelago is a vast assemblage of islands of coral formation, 

 raised so little above the surface of the ocean that it seems 

 possible that a violent storm might render them a mere 

 wreck, and destroy the vegetation and the comparatively few 

 people that are now found on them. The Gambier Islands, 

 which form a portion of the archipelago, are, however, of a 

 different character, being of volcanic formation, and therefore 

 mountainous. Pitcairn Island, noted for being the refuge of 

 the mutineers of the Bounty, who intermarried with the native 

 women, and whose descendants number about 200, is also of 

 volcanic origin, and is possessed of a rich and fertile soil. 

 Easter Island, a small island which may also be compared to 

 Jersey in point of size, contains the craters of some extinct vol- 

 canoes, and some curious colossal statues, of which there is 

 not even a legend current among the present inhabitants in 

 commemoration of those who made them and of the purposes 

 for which they were made. 



The maps that accompany this lesson show the relative posi- 

 tion of Australia and the islands in the centre and eastern part 

 of Oceania. For the position of the islands of Malaysia the 

 reader is referred to the Map of Asia, which is given in page 

 120, Vol. III., of the POPULAR EDUCATOR. 



LESSONS IN CHEMISTRY. XXXIII. 



ALDEHYDES KETONES ACIDS. 



ALDEHYDES occupy a place between the alcohols and the vege- 

 table acids. They are the result of the imperfect combustion 

 of the alcohol, by which some of its hydrogen is removed ; hence 

 the origin of the word (aZcohol deTM/cZrogenated). They readily 

 absorb oxygen, forming the acid, thus 



Alcohol. Aldehyde. 



2C 3 H O + O, = 2C..H.O + 2H..O. 



Aldehyde. Acetic Acid. 



C 3 H 4 O + O = C a H t O.,. 



Acetic aldehyde may be procured by distilling a mixture of 6 

 parts of sulphuric acid, 4 of alcohol (specific gravity 0'850), 4 

 of water, and 6 of finely-powdered black oxide of manganese. 

 The distillate is several times rectified from calcium chloride. 

 Acetic aldehyde is a colourless liquid, possessing an irritating, 

 pungent odour. One of its most prominent characteristics is 

 its action on a salt of silver. To the solution of the silver salt 

 should be added a little ammonia, and then boiled with the 

 aldehyde. The oxygen of the salt goes to the aldehyde to form 

 an acid ; this acid combines with the ammonia, and the metal is 

 deposited as a bright mirror film on the sides of the vessel. 

 With ammonia a crystalline compound, C,H S (NH 4 )O, is formed; 

 and a third distinctive action is their combining with hydrosodic 

 sulphite, the compounds being soluble in water. 



Propionic Aldehyde (C 3 H O), Butyric Aldehyde (C 4 H 8 O), and 

 the others of this series are of no great interest. 



KETV.NTES OB ACETONES. 



Ketone is the name applied to the group; acetone is the 

 ketone of acetic acid. 



As the other ketones have little interest, we shall only describe 

 Acetone (C 3 H 6 0). It may be obtained by distilling a mixture 



of calcic acetate with an excess of quicklime. The reaction ia 

 thus expressed : 



Calcic Calcic 



Acetate. Carbonate. Acetone. 



Ca2C.,H 3 O, = CaCO, + C 3 H 8 O; 



or the distillation of sodic acetate will yield it in a state of 

 purity 



Sodio Sodic 



Acetate. Carbonate. Acetone. 



2(NaC 3 H,O, 1 ) = Na a CO s + C 3 H 6 O. 



The liquid ia colourless, possessing a pleasant ethereal odour. 

 It much resembles the aldehydes. However, it will not absorb 

 oxygen to form an acid. When heated it gives off a vapour 

 which burns with a luminous flame. Potassic hydrate decom- 

 poses this vapour, thus 



Acetone. Potassic Hydrate. Potassio Acetate. Marsh Gas. 



fH * f "*" TTl^ = KC 3 H 3 O., + TT* 1 



^ s ) ^ ) ** ) 



This reaction shows the likeness which acetone bears to acetic 

 aldehyde. Under similar circumstances this latter body behaves 

 thus 



Aldehyde. Potassio Hydrate. Potassio Acetate. Hydrogen. 



Cfl ^' | + ^JO = KC a H 3 O a + ^i 

 ORGANIC ACIDS. 



Acetic Acid (H,C 2 H 3 O 2 ) is the most important of the claas. 

 It appears in the juices of several plants ; but for commercial 

 purposes it is artificially prepared by causing the alcohol in 

 various fermented liquors to become oxidised. 



Vinegar owes its acidity to acetic acid, of which it contains 

 about 6 per cent. The process of manufacture in England is 

 this : Malt wort is allowed to ferment until all the sugar has 

 become alcohol. The yeast is then removed as thoroughly as 

 possible, and the " wash " is allowed to trickle in at the top of 

 large vats, which are filled with wicker-work. The vat must 

 have been in operation some time, in order that the slimy mould 

 popularly called mother of vinegar may grow on the basket- 

 work. In a new vat, some old wicker-work covered rvith the 

 mould is introduced. This mould is a vegetable organism 

 mycoderma aceti -and plays a similar part as the yeast did in 

 the alcoholic fermentation. Near the bottom of the vat a 

 number of holes are bored, which admit the air. Since the 

 temperature of the vat rises during the operation, a current is 

 induced, and the air entering at the holes in the bottom, 

 ascends, meeting the alcohol as it trickles over the wicker-work, 

 which in the presence of the plant it oxidises into acetic acid 



C,H O + O, = H a O + C a H 4 O,. 



The best vinegar is prepared, in France, from wine. This is 

 readily made by allowing vats of wine to be acted on by the air 

 in a shed kept at a temperature of 30. When a few gallons of 

 vinegar are drawn from a vat, fresh wine is added to the same 

 amount. About a fortnight is required to complete the process. 

 In Germany and other countries, where there is no duty on 

 spirit, alcohol is mixed with an infusion of malt, and then sub- 

 mitted to oxidisation in the vats described. 



Acetic Acid is also furnished in the destructive distillation of 

 wood. It is then known under the name of pyroligneous acid. 

 We have referred to " wood naphtha " as one of the products. 

 After this has been driven off, acetic acid is found with the tarry 

 matters in the retort. By adding milk of lime or sodic carbo- 

 nate, the acetic acid is extracted as an acetate of lime or soda. 

 The salt is cautiously roasted, in order to free it from the tarry 

 matters ; then dissolved in water and crystallised. To set the 

 acetic acid free, sulphuric acid is added, and the mixture distilled. 

 The greatest portion of acetic acid used in this country is pro- 

 cured in this manner. 



Properties. Below 17 Cent., the normal acid does not exist 

 in a liquid state, but appears as crystals, in plates which radiate 

 from a centre. Hence it is known as glacial (ice-like) acetic 

 acid. It is remarkable that on being diluted, its density 

 increases until about one-third of its weight of water is added ; 

 then it begins to obey the ordinary law, and its density de- 

 creases for further additions of water. 



The acetates are largely used in the arts and in medicine. 

 Aluminum acetate is used by the dyer and the calico-printer as 

 a mordant. A solution of this salt is thickened by gum, and 

 thus applied to the fabrics, which are then hung up in a warm, 

 moist atmosphere. Iron, zinc, and manganese acetates are 

 also used as mordants. 



