124 SCIENTIFIC AMUSEMENTS. 



if a little white of egg be mixed with four or five times its bulk 

 of water, and some of the clear solution (filtered if necessary) 

 gently heated in a test-tube, the fluid will by and by become 

 turbid, because the " albumin " contained in the white of egg is 

 affected by heat chemically, and converted into a somewhat dif- 

 ferent substance not soluble in water. White of egg and other 

 albuminous fluids (like blood deprived of the clot and red sub- 

 stance) are used in the arts to clarify sugar, syrups, jellies, and the 

 like ; as the albumin solidifies on heating the liquid, it catches up 

 and entangles small suspended particles, and enables the liquid to 

 be strained or filtered much clearer and brighter than would 

 otherwise be possible. 



Take some chrome alum., and dissolve it in water; to a tea- 

 spoonful of the purplish-green solution, add drop by drop caustic, 

 soda solution ; a green precipitate will first form, which on addi- 

 tion of more soda (with stirring) will redissolve to an emerald- 

 green fluid ; on cautiously boiling this in a test-tube, the liquid 

 will soon become turbid, and on standing a short time will allow a 

 green precipitate to subside, whilst the supernatant liquid is colour- 

 less. This arises in virtue of a chemical change taking place in 

 the nature of the dissolved compound giving the green colour, 

 solely through the action of heat. 



Another instance of every day occurrence is the effect of heat 

 upon "hard" natural water; a "crust" or precipitate of cal- 

 careous matter is produced on boiling such water, forming the 

 " furr " inside a tea-kettle, and the " boiler crust " or " scale " in 

 an ordinary steam boiler ; this arises from the chemical action 

 taking place under the influence of heat on the substances dissolved 

 in the "hard" water (vide Expt. 155). 



Expt. 123. To test for Grape Sugar. Prepare some solution 

 of sulphate of copper, add to it some powdered tartaric acid, and 

 then add enough solution of caustic soda to convert the whole into 

 a clear pretty deep blue fluid ; if not clear at first, add more tar- 

 taric acid and then more soda, and shake up or stir well. To a 

 little of this blue solution in a test-tube add a few drops of a weak 

 solution of grape sugar, or of treacle, honey, or golden syrup, largely 

 diluted with water. On heating the mixture a precipitate will be 

 formed in virtue of chemical action ; according to the strength of 

 the solution and other circumstances, the colour of the precipitate 

 will be an orange-yellow, brownish deep red, or dark reddish- 

 brown, in all cases very different from the original blue fluid. 

 By this test you may prove the presence of grape sugar in the juice 

 of a sweet grape, or in the liquid got by cutting up a fig or a date 

 or a raisin in shreds and soaking these in water, the liquid being 



