SOA 



SOA 



SNOW. Congealed moisture : it 

 is produced whenever a cold wind 

 below 32^ Fahrenheit acts upon the 

 moisture of warmer clouds. It is an 

 excellent coverin},' for winter crops, 

 protecting them from the winds and 

 sudden changes of winter ; it also 

 protects roots and the bark of trees 

 from mice. 



SOAP. "This useful compound 

 is obtained by the action of alkaline 

 upon oily substances. There arc, 

 accordingly, a great variety of soaps ; 

 but those commonly employed uiay 

 be considered under the heads of, 1. 

 Fine white soa[)s, scented soap, &c. ; 

 2. Coarse houseliold soaps ; 3. Soft 

 soaps. The materials used in the 

 manufacture of white soaps are gen- 

 erally olive oil and carbonate of soda : 

 the latter is rendered caustic by the 

 operation of quicklime, and the solu- 

 tion thus obtained is called soap lye. 

 The oil and a weak lye are first boil- 

 ed together, and portions of stronger 

 lye are gradually added till the soap, 

 produced by the mutual action of the 

 oil and alkali, begins to become tena- 

 cious and to separate from the water ; 

 some common salt is then generally 

 added to promote the granulation and 

 perfect separation of the soap : the 

 fire is then drawn, and the contents 

 of the boiler allowed to remain for 

 some hours at rest, so that the soap 

 may more completely collect. When 

 it is perfect it is put into wooden 

 frames or moulds ; and when stiff 

 enough to be handled, it is cut into 

 oblong slices and dried in an airy 

 room. Perfumes are occasionally 

 added, or various colouring matters 

 stirred in while the soap is semiflu- 

 id, to give it a mottled appearance. 

 The Spanish soap is marbled by stir- 

 ring into it a solution of sulphate of 

 iron, which is decomposed by the 

 soap, and black oxide of iron separ- 

 ated in streaks and patches through 

 the mass. The action of the air con- 

 verts the exterior into red oxide, 

 while the interior long retains its 

 black colour ; hence a slice of this 

 soap presents a black mottled centre, 

 surrounded by a reddened external 

 layer. 



726 



" Common household soaps are 

 made chiefly of soda ash and tal- 

 low ; or if potash is used, a large ad- 

 dition of common salt is made to 

 harden the soap, wliich it probably 

 effects by the transference of soda. 

 Yellow soap has a portion of rosin 

 added to it. Soft soaps are generally 

 made with potash, instead of soda, 

 and fish oil. I'lic common soft soap 

 is a compound of this kind ; it has a 

 tenacious consistence, and appears 

 granulated. Soap is soluble in pure 

 water and in alcohol ; the latter so- 

 lution jellies when concentrated, and 

 is medicinally known under the name 

 of opodeldoc. When carefully evap- 

 orated the soap remains in a gelati- 

 nous state, which forms, when dry, 

 the article sold under the name of 

 transparent soap. 



" The earths and common metalUc 

 oxides form insoluble soaps ; and, ac- 

 cordingly, these are precipitated when 

 earthy and metallic salts are added 

 to solution of soap. It is the sul- 

 phate of lime and carbonate of lime 

 in common spring water which thus 

 render it unfit for washing, and give 

 it what is termed hardness ; and, upon 

 this principle, a spirituous solution 

 of soap is a simple and valuable test 

 of the fitness of any river or spring 

 water for the purposes of the laundry. 

 If it merely renders the water slight- 

 ly opalescent, as is the case with 

 rain and other soft waters, it may be 

 used for washing ; but if it become 

 milky, it is usually too hard to be 

 conveniently employed ; and when 

 we wash or shave with hard water, 

 the separation of the insoluble cal- 

 careous soap is extremely disagree- 

 able ; it adheres to the skin, and soils 

 instead of cleansing it. 



"The chemical nature of soap has 

 been laboriously examined by Chev- 

 reul, who has shown that the alkali 

 in the process of saponification con- 

 verts the oil into peculiar acids, as he 

 terms them ; the elain of the oil form- 

 ing o/e;t ac»/, and the stearin margar- 

 ic acid : so that soluble soaps are oie- 

 ates and margarates of soda and pot- 

 ash. He has enumerated several 

 other fatty acids similarly produced. 



