AUXILIARY-AIR TYPE AIRFLOW FUME HOODS For
AIR-CONDITIONED LABORATORIES
KEWAUNEE
REPORT FOR ANALYTICAL CHEMISTS
on actual production samples in order that the method may be exposed to all the possible interferences it will be confronted with in actual use. It is also important to have the production samples used cover the widest expected concentration range, and at least three, preferably more, concentrations should be employed. A favorite trick of the statistician is played on the analyst who boasts that his analyses are "right." The statistician finds out what the er-
that you have improved the analysis, without introducing some new and troublesome aspect. Again a designed experiment, utilizing both methods on several different lots, is called for. This will afford a statistically sound test of significance of any observed differences in the analyses by the two methods. Note carefully that I did not specify several different concentrations of a synthetic sample of known composition and no impurities. It is very important to evaluate methods L
Interférer 1 Interférer
2
Interférer
3
H
L L
H H
L H
L
H H
L
L
H
L H L H L H L H L H L H L H L H
pH
3 26 20 15 25 17 32 22ijT 14 7 19 27 18 8 31 H 13 2 30 10 23 11 5 1 12 28 29 21 16 24 6 L
Concentration
1\
Figure 3 .
Factorial design to estimate effects of v a r i a b l e s
H
Interférer 1 H
Interférer 2 Interférer 3 Kewaunee Auxiliary-Air Type A i r f l o w Fume Hoods operate on a ratio of 5 0 % room air a n d 5 0 % a u x i l i a r y air. When operating at the m i n i m u m face velocity of 5 0 F P M , these hoods exhaust only 2 5 C F M of air per square foot of sash opening from the laboratory, w i t h the other 2 5 C F M of air per square foot of sash opening obtained f r o m a n a u x i l i a r y air source.
L
H
H
L H
L
L
H
L H
L
H L H L H L H L H L H L H L H L
PH Concentration
2 5 25 26
H Figure 4 .
24 31
1 4
L
7 14 13 17
8 28 19 3 0 18 23
16 2 9 21 3 2
15 20
KEWAUNEE
24 A
·
ANALYTICAL CHEMISTRY
6 10 12 11
Factorial design which allows estimation of errors
Write for complete information on these n e w A i r f l o w Fume Hoods t o d a y !
Circle No. 68 on Readers' Service Card
9 27
3 22
A n additional a d v a n t a g e only available with Kewaunee A u x i l i a r y - A i r Type A i r f l o w Fume Hoods is that all air (both room a n d a u x i l i a r y ) enters through the hood face a n d is virtually 1 0 0 % effective in s w e e p i n g fumes back to the baffle exhaust openings.
KEWAUNEE MFG. COMPANY 5090 S. Center St., Adrian, Mich.
L
Figure 5 .
Typical e x a m p l e o f variations in analysis
