184 



Here again, as in the soils and also in the efflorescence taken from the 

 surface of the soil, magnesium compounds exceed those of Calcium. 

 Sodium carbonate is present in small quantity, the amount being ap- 

 parently less than in the water from Thebus dam. 



The latter yielded the following results in grains per gallon : 



Total salts 45'2 



Sodium chloride 6'3 



Carbon dioxide in combination 12'8 



The water from the dam contains but small quantities of lime and 

 magnesia, so that in all probability the carbon dioxide in it was combined 

 with soda, forming sodium carbonate, and the use of this water, unless 

 accompanied by effective drainage, would therefore tend to increase in the 

 soil that most injurious form of alkali, " black brack." The water from 

 the pit, on the other hand, had its carbon dioxide combined with lime and 

 magnesia principally. 



On page 266 of King's " Irrigation and Drainage " will be found a 

 table, computed from Bulletin 29 of the Oklahoma Experiment Station, 

 page 4, showing the composition of alkaline waters that may be regarded 

 as safe and those which are considered unsafe to use for irrigation. 



Bearing in mind that sodium carbonate represents what is called 

 " Black Alkali " in King's tables, and that sodium chloride and sulphate 

 together constitute " White Alkali," it will be seen that the amounts in 

 the pit water are as follows: 



Black Alkali '095 parts per thousand. 



White Alkali -188 



Now, according to the tables in King's book, a water may be con- 

 sidered safe if the black alkali which is the most harmful constituent- 

 does not exceed, say, '100 parts per thousand, provided the white alkali be 

 not too high, but that if the former exceed the figure just mentioned the 

 water cannot be regarded as safe. White alkali is less injurious, and up 

 to about '500 parts per thousand may be passed, but beyond this limit, 

 even though the black alkali may be low (as in the case of sample 741 of 

 King's tables, where the black alkali is "026 and the white '818 per thou- 

 sand), it would be risky to make constant use of the water. 



In the sample of water from the pit at Thebus the white alkali was 

 well within the limits of safety, but the black alkali was on the border 

 line, and in the sample of water from the darn the limit was apparently 

 exceeded, although the smallness of the sample sent prevented this being 

 definitely ascertained. 



It must, of course, be kept in view that the figures with which the 

 analytical results of the Thebus water are compared are derived from ex- 

 perimental data obtained in Europe and America. If the facilities for 

 making such very necessary experiments existed here, figures obtained 

 under local conditions might be found to differ from those obtained in 

 Europe and in the United States, but this very fact makes it all the more 

 necessary to exercise great caution in proceeding with extensive irrigation 

 schemes. 



DIVISION OF ROBERTSON. 



A series of determinations, similar to those conducted in regard to the 

 Thebus soils, have also been made in connection with the soil of the 

 Government Experiment Station at Robertson. When dealing with the 

 determinations of plant fuod in the soils of that locality, it was stated 



