640 LABORATORY HINTS 



(1) THE BIOLOGICAL EXAMINATION. 



This enables us to determine the absence or presence of lowly 

 organisms, bacteria, jDrotozoa, larvae, &c. 



The following are common and should be looked for : — 



In impure water In sewage 



Vorticella Rotifera Carcliesium 



Cienothrix Ulothiix Oscillatoria nigra 



Asterionella Alg.=e Leptomitus 



Diatoma Spirilla Sphterotikis natans 



Actinophrys Spirogyra Beggiatia 



Protocoeccus Gammarus pulex Ulva latissinia 



Euglena Cyclops Enteromorpha 



Oscillaria Water bear Infusoria 



Desmids Bomina longitirastis 



(2) THE PHYSICAL EXAMINATION. 



The reaction should be neutral. 



Add a little neutral litmus to the sample. 



COn will turn it red. 



Remember that acid waters attack lead and iron pipes. 



The colour should be a pale blue or green. 



Half till a two-feet tube and la}- it upon tlie table. 



Look through the upper lialf which is colourless. 



Look through the lower half ^\'hich assumes the colour of the water. 



It should be odourless. To test it warm to about 37° C. 



Certain mineral waters contain HoS, also given off by beggiatoa and 

 crenothrix. 



Volvox and uroglena give a fishv odour. 



Anab^ena and rivularia give a grass v odour. 



Asterionella and diatoma give an aromatic odour. 



There should be no sediment. If there is such it should be 

 examined under the microscope. 



(3) THE BACTERIOLOGICAL EXAMINATION. 



This indicates the presence or absence of pathogenic and other 

 bacteria and the number thereof. These are : — 

 (i) Normal inhabitant bacteria. 



(2) Accidental soil bacteria. 



(3) Intestinal bacteria. 



Sunlight reduces their number if the water is shallow and the 

 exposure prolonged. 



Cold inhibits their growth and warmth stimulates it. 



Presence of food materials stimulates their growth. 



Most bacteria tend to settle at the bottom and so thus assist in 

 self-purification of the water. 



Typhoid and cholera organisms die out if stored long, about twelve 

 weeks. 



