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Ann. Acad. Scient. Fennicse
A.IT.
101
powder by the spray method with a laboratory machine (NITRO Atomizer).
Samples 10—15 were taken from the product of the two factories of the
Kuivamaito Oy. They were similarly dried by the spray method on a
commercial scale from skim milk.
The milk powder was burned to a semicarbonized form over Bunsen
burners in porcelain evaporation dishes. The final ashing was done in quartz
dishes at 450°C in a muffle furnace. For each analysis 15 g of ash, corresponding to about 2 1 of milk, was used.
In the chemical separation of Sr the procedure of Bryant, Morgan and
Spicer (14) was followed, except for the following phases.
The manipulations corresponding to § 8 of Appendix I 2 were made as
follows: strontium wasprecipitated as carbonate by adding solid ammonium
carbonate and heating on a water bath. The precipitate was separated by
centrifugation, dissolved in a small amount of 6 N HCl and transferred to
a 100 ml polyethylene bottle with 20 mi of water. 1 ml of yttrium carrier
was added and Sr-Y equilibrium allowed to form for at least 14 days.
§ 9 was omitted.
§ 10 was changed to the following: The solution was transferred from the
bottle to a 40 ml centrifuge tube and madealkaline with CO,-free ammonia.
The clear centrifugate was transferred to a 100 ml measuring flask for a
flame photometric determination of strontium. The precipitate was dissolved
in 6 N HNO, and diluted to 10—15 ml, 10 ml of strontium-carrier was added
as a hold-back carrier and a new ammonia precipitation was performed.
(Strontium carrier was added to prevent co-precipitation of the remaining active strontium on the highly absorbing Y(OH), precipitate.) The centrifugate was rejected. The time of the first yttrium precipitation was
noted.
Strontium recovery was determined by a flame photometer (Zeiss) using
the wave length 460.7 mu. The determinations were based on 3 strontium
standards.
The radioactivity of the yttrium precipitation was determined with a
Tracerlab anticoincidence counter CE 14, which had a background of 1.2—
0.6 ¢/min.
.
Calcium was determined as the oxalate from a part of the samples gravimetrically by the method of Bryantef al. (14), from a part of the samples
by dissolving the oxalate precipitate in 2 N H,SO, andtitrating with 0.1 N
potassium permanganate.
The dry weight of the milk powder was determined by drying it for 24
hours at 105°C because the humidity of the milk powder samples varied
from 1.9 to 3.8 %.
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