STABILIZATION OF PHOSPHATE EST SEA WATER 



75 



Experiments 5 and 6 



Experiment 5 was designed to obtain more 

 nearly exact information on the effect of freezing 

 on the changes in the concentration of inorganic 

 phosphorus by minimizing the delay inherent in 

 drawing and freezing a large number of samples. 

 As in experiment 4, samples were drawn from 

 Offat's Bayou as rapidly as possible and without 

 filtering. The samples were frozen immediately. 

 Again, the molybdate reagent was added to the ini- 

 tial set, which was analyzed immediately on return 

 to the laboratory. In each, the molybdate reagent 

 was added to the sample as it was placed in the 

 water bath so as to minimize changes which might 

 take place in the period of thawing. 



In this experiment, the first set of samples was 

 analyzed 90 minutes after freezing, the last set 4% 

 hours later (table 6). With this technique, no 

 differences are evident either in the t test or in the 

 F value of the analysis of variance. 



Table 6. — Changes in inorganic-phosphorus concentration 

 of sea water occurring at subzero temperatures 



A. VALUES IN ji'ORAM ATOMS OP PO<-P FEB LITEB 



Time interval 



Initial. 

 Hi hrs 

 3H hrs 

 AH hrs 

 6?ihrs 



Number 

 inset 



Mean 



2.90 

 2.65 

 2.70 

 2.95 

 2.80 



Standard 

 deviation 



Fiducial 

 limits (t.u) 



B. COMPARISON OP MEAN OP INITIAL SET WITH MEANS OP 

 SUBSEQUENT SETS 



O. ANALYSIS OP VARIANCE 



The same techniques were employed in experi- 

 ment 6 as in experiment 5, but the samples were 

 held for a longer period of time, as shown in table 

 7. Here, again, the rapid freezing techniques 

 minimized changes during the period of collection, 

 so that no significant changes in the concentrations 

 of inorganic phosphorus were evidenced in the t 

 test. The difference shown in the F test of the 

 analysis of variance, being greater within than 

 between sets, is probably due to particulate 

 material, since these samples were not filtered. 

 The variance between sets is at a minimum. 

 From these experiments, it is apparent that rapid 

 freezing and holding of samples at subzero tem- 

 peratures effectively stabilizes the inorganic-phos- 

 phate ratio, so permits of analysis even weeks after 

 collection with greater assurance of accuracy than 

 if any delay is encountered between collection and 

 analysis. 



Table 7. — Changes in inorganic-phosphorus concentration 

 of sea water occurring at subzero temperatures 



A. VALUES IN JJ-GBAM ATOMS OP PO|-P FEB LITEB 



Time interval 



Initial. 



2 hrs.. 

 3H hrs 

 1 day.. 



3 days. 

 7 days. 



Fiducial 

 limits (f.oi) 



0.178 

 .201 

 .097 

 .243 

 .283 

 .231 



B. COMPARISON - OP MEAN OP INITIAL SET WITH MEANS OP 



SUBSEQUENT SETS 



Time Interval 



2 hrs.... 

 3)i hrs. 

 1 day... 



3 days.. 

 7 days. . 



Degrees of 



freedom 



15 

 12 

 15 

 15 

 14 



F < 1 between i 



