E527 (Ammonium hydroxide) is a chemical compound, a solution of ammonia in water. 

It is in the form of a liquid with a pungent ammonia odour, easily soluble in water, weakly alkaline, with an ionisation constant. The percentage of ammonia generally varies from 10% to 50%.

What it is used for and where it is used

Food

Ingredient included in the list of European food additives as  E527, acidity regulator and pH control agent. It is generally considered a safe component.

Cosmetics. 

It is a restricted ingredient III/4 as a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009

Buffering agent. It is an iingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing, in practice a pH stabiliser that can effectively resist instability and pH change.

Denaturant. The ionic or polar molecules of this ingredient included in formulations that interact with protein groups, modulate the properties of the solution to suit specific needs.

Pharmaceutical.

 It relieves pain, itching and irritation caused by insect bites.

Chemistry. 

Analytical reagent, neutraliser, alkaloid leaching agent, tests and determines nickel and copper. Determines colorimetry. Precipitates hydroxides of various elements, preparation of ammonium compounds. Can react with silver chloride to generate silver ammonia [Ag(NH3)2]Cl, which can dissolve some insoluble salts. Generates ammonium salt which, when burned, generates nitrogen, in reaction with acid. 

Typical optimal commercial product characteristics  Ammonium hydroxide

Appearance	Liquid with a pungent odour of ammonia
Density	0.91 g/mL at 20°C
Boiling Point	36°C
Melting Point	-77°C
Explosive limit	27%
NH3	20%
Residue	0.3%
Chromaticity	80
Safety

• Molecular Weight  H₅NO    NH₄OH
• Molecular Weight     35.046 g/mol
• Exact Mass   35.037113
• CAS  1336-21-6
• UNII    
• EC Number   215-647-6
• DSSTox Substance ID DTXSID4020080
• IUPAC  azanium;hydroxide
• InChI=1S/H3N.H2O/h1H3;1H2 
• InChl Key      VHUUQVKOLVNVRT-UHFFFAOYSA-N
• SMILES   [NH4+].[OH-]
• MDL number  MFCD00066650
• PubChem Substance ID    
• ChEBI  18219
• ICSC    0215
• Beilstein   3587154
• RTECS   BQ9625000
• UN   2672

Synonyms:

• Ammonia aqueous
• Ammonium hydroxide solution
• Aquammonia