You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

On the origin of sharp peaks in the X-ray diffraction patterns of xanthan powders. A series of xanthans containing different levels of the charged group pyruvate has been examined. The X-ray diffraction patterns of the powders of these materials had different levels of a sharp pattern superimposed on an amorphous background. As the moisture content increased so the intensity of the sharp pattern increased up to a level between 20% and 40% moisture content where the sharp pattern disappeared. X-ray diffraction pattern identification software and an inorganic X-ray diffraction database showed the origin of the sharp peaks to be due to sodium sulphate polymorphs. The behaviour of the xanthans was thought to be due to the differences in charge on the molecule; however, the increase in the crystalline component observed with increased amounts of water was unexpected. The possibility of the drying of samples was considered but the interplay between ions, the charged polymer and the water present was considered necessary to more closely describe the results.
{"Chemical": ["sodium sulphate", "pyruvate"]}