Herzberg filtration speed: The time taken to filter $\pu{100 mL}$ water at $\pu{20 ^\circ C}$ through a filter area of $\pu{10 cm2}$ at a constant pressure of $\pu{5 cm}$ water column (Thomas Scientific).
The values are given in seconds. So, the example OP has given has Herzberg filtration speed of $\pu{375 s}$. That means the relevant filter paper takes $\pu{375 s}$ to filter $\pu{100 mL}$ of water under above Herzberg filtration conditions. Thus your understanding is partially correct (except for $\pu{10 cm}$ water column):
If that is a reliable description then it looks like "375 herzberg" means that it took $\pu{375 s}$ for $\pu{100 mL}$ of water with a $\pu{10 cm}$ constant head to flow through a $\pu{10 cm2}$ filter, which means that more Herzberg = less flow.
Keep in mind that the temperature is important (Ref.1). This measurements are done at only $\pu{20 ^\circ C}$. This reference described Herzberg's research as:
Herzberg used a constant-head apparatus, based on the principle of the Mariotte flask, which forced water through a horizontal disk of filter paper $\pu{10 cm2}$ in area and discharged it into a measuring flask. With a head of $\pu{5 cm}$ of water at $\pu{20 ^\circ C}$, the instrument was used to measure either the time of filtration of $\pu{100 ml}$ of water or the volume of water filtered in $\pu{1 minute}$. He reported a range of filtering rates of $23$ to $\pu{760 ml/min}$ per $\pu{100 cm2}$ of area for 30 filter papers (Ref.2).
Thus, it is safe to assume that the definition given in Thomas Scientific is based on these conditions.
References:
Herman Bogaty, Frederick T. Carson, "Measurements of rate of flow of water through filter paper," Journal of Research of the National Bureau of Standards 1944, 33, 353-362 (PDF).
Wilhelm Herzberg, In Papierprüfung (Paper testing); Fifth Edition, Springer Verlag: Berlin Heidelberg, Germany, 1921 (ISBN: 978-3-662-23207-1).
Herzberg filtration speed: The time taken to filter $\pu{100 mL}$ water at $\pu{20 ^\circ C}$ through a filter area of $\pu{10 cm2}$ at a constant pressure of $\pu{5 cm}$ water column (Thomas Scientific).
The values are given in seconds. So, the example OP has given has Herzberg filtration speed of $\pu{375 s}$. That means the relevant filter paper takes $\pu{375 s}$ to filter $\pu{100 mL}$ of water under above Herzberg filtration conditions. Thus your understanding is partially correct (except for $\pu{10 cm}$ water column):
If that is a reliable description then it looks like "375 herzberg" means that it took $\pu{375 s}$ for $\pu{100 mL}$ of water with a $\pu{10 cm}$ constant head to flow through a $\pu{10 cm2}$ filter, which means that more Herzberg = less flow.
Keep in mind that the temperature is important (Ref.1). This measurements are done at only $\pu{20 ^\circ C}$. This reference described Herzberg's research as:
Herzberg used a constant-head apparatus, based on the principle of the Mariotte flask, which forced water through a horizontal disk of filter paper $\pu{10 cm2}$ in area and discharged it into a measuring flask. With a head of $\pu{5 cm}$ of water at $\pu{20 ^\circ C}$, the instrument was used to measure either the time of filtration of $\pu{100 ml}$ of water or the volume of water filtered in $\pu{1 minute}$. He reported a range of filtering rates of $23$ to $\pu{760 ml/min}$ per $\pu{100 cm2}$ of area for 30 filter papers (Ref.2).
Thus, it is safe to assume that the definition given in Thomas Scientific is based on these conditions.
References:
Herman Bogaty, Frederick T. Carson, "Measurements of rate of flow of water through filter paper," Journal of Research of the National Bureau of Standards 1944, 33, 353-362 (PDF).
Wilhelm Herzberg, In Papierprüfung (Paper testing); Fifth Edition, Springer Verlag: Berlin Heidelberg, Germany, 1921 (ISBN: 978-3-662-23207-1).
@ Andrew: I have edited to give additional infomation. Although Thomas Scientific is a vendor, they have followed exactly what Herzberg has done to find various flow rates of various filter papers. I think that would clear OPs doubts about definition.More
Thanks; your source is actually one of the two links I cited in my question ("this old paper on filtration flow rate measurement"). The thing is, it describes Herzbergs work, but otoh it doesnt appear to define a named unit based on that work (although I could not find an English version of More
Herzberg filtration speed: The time taken to filter $\pu{100 mL}$ water at $\pu{20 ^\circ C}$ through a filter area of $\pu{10 cm2}$ at a constant pressure of $\pu{5 cm}$ water column (Thomas Scientific).
The values are given in seconds. So, the example OP has given has Herzberg filtration speed of $\pu{375 s}$. That means the relevant filter paper takes $\pu{375 s}$ to filter $\pu{100 mL}$ of water under above Herzberg filtration conditions. Thus your understanding is partially correct (except for $\pu{10 cm}$ water column):
Keep in mind that the temperature is important (Ref.1). This measurements are done at only $\pu{20 ^\circ C}$. This reference described Herzberg's research as:
Thus, it is safe to assume that the definition given in Thomas Scientific is based on these conditions.
References:
Herzberg filtration speed: The time taken to filter $\pu{100 mL}$ water at $\pu{20 ^\circ C}$ through a filter area of $\pu{10 cm2}$ at a constant pressure of $\pu{5 cm}$ water column (Thomas Scientific).
The values are given in seconds. So, the example OP has given has Herzberg filtration speed of $\pu{375 s}$. That means the relevant filter paper takes $\pu{375 s}$ to filter $\pu{100 mL}$ of water under above Herzberg filtration conditions. Thus your understanding is partially correct (except for $\pu{10 cm}$ water column):
Keep in mind that the temperature is important (Ref.1). This measurements are done at only $\pu{20 ^\circ C}$. This reference described Herzberg's research as:
Thus, it is safe to assume that the definition given in Thomas Scientific is based on these conditions.
References:
More
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