Summary for nitric acid concentration Discussion
Specific gravity can be used to estimate nitric acid concentration, but only in the right context. In this thread, Colin Scott Wayne asked whether a specific gravity gauge can reliably measure nitric acid concentration. The reply explains that if the material is raw nitric acid dissolved in water, then yes, specific gravity is a valid way to gauge concentration. However, if the acid is in a process tank, the reading will not be reliable because other dissolved materials change the density and skew the result. The answerer points Colin to another thread, 41654, for the process-tank case. The practical takeaway is that specific gravity works for relatively pure nitric acid solutions, but not for mixed process baths where other chemicals are present.
Q. Can you reliably measure nitric acid concentration with specific gravity gauge?
Colin Scott Wayne
Employee – SAN DIEGO, California
October 2, 2024
A. Hi Colin.
If you mean as a raw material, i.e., pure nitric acid dissolved in water, yes you can.
If you mean within a process tank, no, because the other materials dissolved in the tank will effect the density/specific gravity. If that is your case, see thread 41654.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
⇩ Similar, related, Q&As — oldest first ⇩
Q. 1. Where can I get information relating baumé (specific gravity) to percent concentration for various acids?
2. I have recently seen the expression “42% absolute nitric acid”. What does this mean and how does it relate to “percent concentration” and “baumé”?
3. The problem is that we are etching a carbon steel mandrel
(12L14) out of a 6061 aluminum part and severely attacking the aluminum surface. The etchant currently being used is a
“concentrated” nitric acid marked “50%”. All former experienced personnel retired several years ago and are not available to answer the obvious question.
Richard Basil
– Redondo Beach, California
1998
A. baumé is another method of measuring specific gravity. There are conversion tables for it.
42 degree nitric is 67.18% nitric. This is a common commercial strength as it gives of a lot of NOx (a poisonous red cloud) at progressively higher strengths.
50% nitric would have a baumé around 35.
Most people use 50 % as half and half water and 42 baumé nitric.
42 Be nitric will severely etch some aluminum alloys, such as those with high copper content.
Some companies will sell a 69 -71% nitric acid which will have a Be around 43 to 43.5 .
If you can get 44 Be nitric, and keep all water out, parts can not even be slightly damp, it will slowly eat the steel and not touch the aluminum.
You might have to add a little ferric chloride
⇦ on
eBay or
Amazon [affil link] or a touch of hydrochloric to speed up the process. There is an extremely fine line of where it will eat the iron and not affect the aluminum alloy. Lab trials will be required.
Can you switch to 1100 aluminum? This is very nearly pure aluminum and it will not be affected by the nitric. A 50 -50 mixture will be able to eat the iron much faster than a 42 or higher Be nitric.
James Watts
– Navarre, Florida
I was recently given a CAR by an aerospace prime contractor regarding the use of 42 degree baumé nitric acid in a solution and told that it did not comply with their specification requiring the use of 68% concentrate nitric acid. I responded that our chemist told me it was the same thing. Certifications from our nitric acid supplier confirmed this to be the case although the material certs did not indicate the degrees baumé. Thank you for clearing this up for me too.
Scott Putnam
metal finishing – Fountain Valley, California
April 14, 2008
A. You also asked for a source for converting % concentration of Nitric acid to sp gravity. Perry’s ChemE Handbook.
contains a table of the specific Gravity of Nitric Acid at various temperatures and % concentration. (note: baumé measurements are made at 60°F.)
Frank Rawolle
– Chula Vista, California