Nitrate test to 2.5 micrograms and a concentration of 1 in 25,000 parts. Devarda's alloy (Copper/Aluminium/Zinc) is a reducing agent. When reacted with nitrate in sodium hydroxide solution, ammonia is liberated. The ammonia formed may be detected by its characteristic odor, and by damp red litmus paper's turning blue, signalling that it is an alkali — very few gases other than ammonia evolved from wet chemistry are alkaline. Aluminium is the reducing agent in this reaction that will occur. Diphenylamine may be used as a wet chemical test for the presence of the nitrate ion. In this test, a solution of diphenylamine
Machine-or-transformation test generally insufficient to make an otherwise ineligible method claim patent-eligible. The PTO Guidance Memo explains that "[t]his means the machine or transformation must impose meaningful limits on the method claim's scope [for it] to pass the test." What makes a limitation meaningful is unstated, but perhaps that concept can be defined in terms of whether the limitation places only an insubstantial limitation on claim scope or preemptiveness. The second corollary is that insignificant extra-solution activity will not transform a patent ineligible principle into a patentable process. The PTO Guidance Memo explains that "[t]his means reciting a specific machine or a