90 LABORATORY MANUAL OF MICROBIOLOGY 



Mercuric Chloride. — A stock solution is prepared and diluted 

 to the desired strength. 



Add 1 part of mercuric chloride to 2.5 parts of commercial 

 hydrochloric acid (40 per cent HgCU in HCl). To prepare 

 a 1:1,000 solution, take 2.5 cubic centimeters of the stock solu- 

 tion and dilute to 1,000 cubic centimeters. Color with dye and 

 label ''poison." 



Transferring Cultures. — Hold the test-tube cultures to be 

 transferred as nearly in a horizontal position as possible. Avoid 

 opening cultures in a current of air. 



All cultures are to be grown in the incubator at 28°C. unless 

 otherwise stated. 



Care of Apparatus. — After using balances, always return 

 weights to their proper places. Do not leave any dust or dirt 

 on balances. 



All solid material, as soil, agar, cotton or filter paper, must be 

 emptied into waste jars and not into the sinks. 



Soil should not be sieved in the laboratory. The greenhouse 

 or potting room may be used for this purpose. 



At the end of the laboratory period return all stock bottles 

 and chemicals to their proper places on the shelves. See that 

 all apparatus is replaced in the lockers and that all gas burners 

 are shut off. Wipe off the table top before leaving. 



Anything left on the desk will be collected after the laboratory 

 period and returned to the store room. 



Cleaning Glassware. — All glassware must be thoroughly cleaned 

 before it is ready to use. Test tubes, Petri dishes, flasks, and 

 similar glassware should be boiled in a 5-per cent soda solution or 

 washed in hot soapsuds until free from organic matter. When it 

 is desirable to use very clean glassware, immerse for 10 minutes 

 or longer if possible in the dichromate solution. 



Potassium (K2Cr207) or sodium dichromate (Na2Cr2- 



Ot) 40 gm. 



Water 150 cc. 



Sulphuric acid (H2SO4) 230 cc. 



Note. — Dissolve the dichromate in warm water and, when cool, add 

 slowly concentrated sulphuric acid. If properly prepared, the liquid should 

 be thick, with small crystals. It may be used repeatedly, provided the 

 crystals are present. 



