SOLDERING 865 



The first time of using there will be a quantity of air in the bell, which is discharged 

 by opening the cock. When the gas has a pungent smell it is fit for use. 



The gas-tap and water-tap are provided with index-plates, which regulate the supply 

 of gas and water to the pump of machine ; they must be partly opened or closed by the 

 person working the machine to suit the requirements. The machine must not be 

 worked with the water-tap open alone. The machine being set to work the gas is 

 urawn down the pipe, which stands above the level of the water, through the other 

 pipe, and is forced into the condenser (D), where an agitator, worked by the spur- 

 wheel (E), revolving rapidly, mixes it with the water which is drawn from the solution- 

 pan o in like manner. When the pressure is up the safety valve will lift, and soda- 

 water may bo bottled from the nose (N). A pressure gauge may be recommended 

 as very useful in enabling the person working the machine to keep the pressure 

 uniform. 



SODIUM. (Symh. Na; Al.Wt. 23.) This metal was discovered by Sir H. Davy, 

 almost immediately after potassium, and by the same means, viz., by exposing a 

 piece of moistened hydrate of soda to the action of a powerful voltaic battery, thu 

 alkali being placed between a pair of platinum plates connected with the battery. 



By this process only very small quantities can be obtained, but processes have 

 since been devised which provide it in almost any quantity, and since the demand 

 for sodium in the manufacture of aluminium by Wohler's process, principally by the 

 exertions of M. C. St.-Claire Deville, the cost of it has been considerably diminished. 

 The process now adopted is the same as that for obtaining potassium. An intimate 

 mixture of carbonate of soda and charcoal is made by igniting in a covered crucible 

 a salt of soda containing an organic acid, as the acetate of soda, &c., or by melting 

 ordinary carbonate of soda in its water of crystallisation and mixing with it, while 

 liquid, finely -divided charcoal, and evaporating to dryness ; this mixture is mixed with 

 some lumps of charcoal and placed in a retort, which is generally made of malleable 

 iron, but owing to the difficulty of getting them sufficiently large, earthenware or fire- 

 clay retorts have been used with success, and sometimes these are lined with or 

 contain a trough of malleable iron. These retorts are so placed in a furnace that they 

 are uniformly kept at a heat approaching to whiteness. 



The principal reaction which takes place in the retort, is the reduction of the soda 

 by the charcoal, which is thus converted into carbonic oxide, which escapes through 

 an aperture in the receiver made on purpose. 



Sodium is a silver- white metal, very much resembling potassium in every respect ; 

 it is so soft at ordinary temperatures that it may be easily cut with a knife or pressed 

 between the finger and thumb ; it melts at 194 Fahr., and oxidises rapidly in the air, 

 though not so rapidly as potassium. Its sp. gr. is 0'972. When placed upon the 

 surface of cold water it decomposes it with violence, but does not ignite the hydrogen 

 which is liberated, xmless the motion of the sodium be restrained, when the cooling 

 effect is much less. When a few drops of water are added to sodium the hydrogen 

 liberated immediately inflames, and such is also the case if it be put on hot water ; 

 when burning it produces a yellow flame, and yields a solution of soda. The principal 

 use of sodium is, as before stated, in the manufacture of aluminium, which is now 

 carried on to a considerable extent. 



SODIUM, BROMIDE OF. This salt resembles the bromide of potassium. 



SODIUM, CHLORIDE OF. See SALT. 



SODIUM, IODIDE OP. This exists in considerable proportion in the ash of 

 burnt sea-weeds. See KEIF. 



SODIUM, OXIDES OP. When sodium is burnt in oxygen gas or in air, two 

 different oxides are produced, via. the protoxide and binoxide. These oxides very 

 much resemble the corresponding oxides of potassium. 



SODIUM, SULPHIDES OP. Several of these are known, resembling the cor- 

 responding salts of potassium, but they are of no importance in the arts. 



SOJA. The legumes of Sofa hispida are used in the preparation of soy, and are 

 imported to this country from India. 



SOIiAWINE. A poisonous alkaloid of doubtful constitution, contained in various 

 plants of the species Solatium, as S. nigrum, 8. Dulcamara, and in the potato (8. 

 tuberosum'). It is remarkable that in the shoots of potatoes which have sprouted 

 in dark cellars the quantity of solanine is greater than in the shoots which have 

 germinated normally. Solanine requires reinvestigation. 



SOZiAZZI JUICE. A name given to the best kind of Spanish liquorice, Solazzi 

 being the maker's name. See LIQUORICE. 



SOIiDERING. The process of uniting together pieces of metal, by the interposi- 

 tion of a fusible alloy, which is called either soft or hard solder, according as its 

 fusing point is low or high. One process is called by its inventor, M. do Eichemont, 



VOL. in. ... 3K 



