TROPICAL AQUARIUM FISHES 113 



tioned, iron is the least injurious and zinc the most, on account of the 

 rapidity of chemical action of salt on this metal. Therefore, galvanized 

 iron is to be particularly avoided, as it is zinc-plated. The author on one 

 occasion could only secure a galvanized pail in which to bring a collection 

 home. As the trip was only three hours and the pail was a well-seasoned 

 one he thought the chances of success were reasonably good. When the 

 can was opened the water showed a slight milkiness and the fishes were 

 nearly dead, although they had not been crowded. On being placed in the 

 aquarium they soon revived. The best metal in which to ship is tin. This, 

 or any other metal, should first receive a coating of asphaltum varnish. 

 Even galvanized iron when asphaltum-coated is safe for journeys of 

 moderate length, but the asphaltum will eventually chip ot¥ and the pail 

 or can should be carefully looked over each time before using. It might 

 be well to say here that the life of tin pails for freshwater will last much 

 longer if coated with asphaltum varnish. A thin coat spread evenly lasts 

 better than a thick one. 



The very best water-shipping medium is a protected glass bottle or 

 carboy. Arrangements can usually be made to rent or borrow a few of 

 these from drinking-water concerns. If possible the water should be 

 taken from several miles out at sea and not near the mouth of any large 

 river. Clear seawater may be stored indefinitely in carboys in a subdued 

 light, although it would be better to first filter it to remove the larger 

 microscopic life. 



Artificial Seawater. Experience varies regarding the use of artificial 

 seawater. This may be due to difiference in the degree of purity of chem- 

 icals used or care in their mixing. The author has not been particularly 

 successful with artificial marine water, although some writers claim it to 

 be better than ocean water because of its freedom from impurities and 

 marine bacteria. The following is a correct working formula for artificial 

 seawater. There are other elements in the ocean, but in such small quanti- 

 ties as to be negligible for our purposes : 



Sodium chloride (Tablesalt) . .2 lb. 85. 23. 18 gr. 



IMagnesium chloride 3.> 55. 13 gr. 



Magnesium sulphate 25. 33. 1 9 8 gr. 



Potassium sulphate 53. 2'^ 10 gr. 



and sufficient wellwater to bring the whole to ten gallons. 



These proportions of salts, expressed in the ^Metric system, would be: 



Sodium chloride 663 grams. 



Magnesium chloride 75 " 



Magnesium sulphate 50 " 



Potassium sulphate 15 " 



Added to 25 litres of wellwater. 



