78 SCIENTIFIC AMUSEMENTS. 



Expt. 73. To make Sherbet (Lemon Kali). In the gasogene 

 above described, the substances employed to generate the gas are 

 kept separate from the aerated water produced, the former being 

 in the upper bulb, and the latter in the lower one ; but when the 

 presence of these substances in the water drunk is not objection- 

 able, a much more simple method suffices to prepare an effervescing 

 beverage. Thus a mixture of powdered tartaric or citric acid, 

 bicarbonate of soda, and sugar may be made and kept in a dry 

 bottle without change ; but on adding a teaspoonful to a tumbler 

 of cold water and stirring up, a vigorous effervescence ensues, and 

 a sort of aerated lemonade results. Such mixtures, flavoured with 

 a little essence of lemon or ginger, &c., are largely used for 

 summer beverages, under the names of sherbet, lemon-kali, &c., 

 but are apt to exert a medicinal action, owing to the presence of 

 the substance formed by the action of the acid on the bicarbonate 

 of soda (tart-rate or citrate of soda). Seidlitz powders, and various 

 patent medicines that effervesce when thrown into water, are 

 essentially mixtures of this kind, together with some powdered 

 saline matter, such as Epsom salts (sulphate of magnesia) added 

 to produce purgative or other medicinal action. 



Many natural spring waters are effervescent, on account of 

 chemical changes going on underground, in virtue of which the 

 water becomes charged with carbonic acid under some degree of 

 pressure (owing to the depth), just as in a gasogene. When 

 much mineral matter is present in the water, a medicinal effer- 

 vescent water results ; many such springs exist in different parts 

 of the world, to which invalids and people out of health resort in 

 large numbers for treatment. When only a little mineral matter 

 is present, the water is often bottled for use as an ordinary 

 beverage ; Apollinaris water and many similar natural slightly 

 effervescent table waters, are fluids of this kind. 



Water impregnated strongly with carbonic acid is capable of 

 dissolving certain substances insoluble in plain water ; much of 

 the lime giving " hardness " to natural water is dissolved in this 

 way. When iron is taken into solution in such water, a "cha- 

 lybeate " spring is formed ; when very much lime is present, this 

 water often forms a calcareous deposit on all objects with which 

 it comes into contact, owing to some of the lime being thrown out 

 of solution (in the form of carbonate of lime), when the water is 

 exposed to the air. What are known as "petrifying springs" 

 mostly act in this way ; a bird's nest, a twig, ferns and flowers, 

 baskets, and similar objects, when exposed to such water, become 

 gradually covered over with a stony coating, and are apparently 

 converted into stone or "petrified." A well-known well of this 



