FACTS ABOUT WATER 269 



Methods of cleaning materials will be found in the table at the end of this 

 section. 



Soap. There are many different kinds of soaps. Perfumed 

 and colored soaps are usually used for toilet purposes. They 

 have perfume added to conceal disagreeable odors. Strong per- 

 fumed soap should be avoided, since a great deal of perfume may 

 have been added to conceal a poor quality of soap. Floating 

 soaps are made by beating air bubbles into the soap. Marine 

 soap is made from palm nut or cocoanut oil, and readily forms 

 lather with sea water. Medicated soap contains a variety of 

 medicinal substances, such as carbolic acid, tar, etc. Scouring 

 soaps usually contain fine sand, ground slate, or pumice. 



To Determine the Kind of Fiber in a Cloth. Concentrated 

 hydrochloric acid will dissolve silk if a piece of silk is heated in it 

 for about two minutes at a temperature of 125 F. 



Wool is dissolved in a 5 per cent solution of potassium hydroxide 

 if the wool is boiled in the solution for about ten minutes. 



Cotton will not dissolve in either .hydrochloric acid or potas- 

 sium hydroxide. If a piece of cloth is made of wool and cotton 

 it is easy to determine the amount of cotton present by dissolving 

 the wool with potassium hydroxide. 



Experiments. Boil a piece of silk in hydrochloric acid. If it will dissolve 

 it is probably true silk. If some of the cloth is left undissolved, test for wool; 

 if no more of the cloth dissolves the remaining part is cotton. Test several 

 pieces of cloth to determine the kind of fiber. 



To distinguish between linen and cotton, heat a piece of cotton and one 

 of linen for two minutes in a concentrated sulphuric acid. Wash with water 

 and soak in dilute ammonia. The cotton will be changed to a jelly-like mass. 

 The linen will hardly be affected. Another method of determining the dif- 

 ference between cotton and linen is by steeping a sample of each for five 

 minutes in a small amount of olive oil. The linen will appear dark and the 

 cotton light if the samples are placed on a dark background. 



To determine the difference between pure and artificial silk, hold a piece 

 of silk in a pair of tweezers and light one end. Pure silk burns slowly with 

 an odor, goes out quickly and leaves a gummy residue. Artificial silk burns 

 rapidly with no odor. True silk turns yellow with nitric acid while artificial 

 silk is not affected. 



Silk is sometimes weighted with tin and other metals. Such material 

 does not burn when the silk is lighted. 



